All praise is due to Allāh, and may the peace and salutations be upon the Messenger, his family and his companions. To proceed;
Indeed Allāh has sent his Messenger ﷺ with the guidance and the truth religion to make it prevail over all religions even though the Mushrikūn hate it. The biography of the Messenger ﷺ is a practical interpretation of Allāh’s ﷻ legislation, which Allāh has revealed onto him and commanded him to follow, as it has come in His statement,
۞ ثُمَّ جَعَلْنَاكَ عَلَىٰ شَرِيعَةٍ مِّنَ الْأَمْرِ فَاتَّبِعْهَا وَلَا تَتَّبِعْ أَهْوَاءَ الَّذِينَ لَا يَعْلَمُونَ
۞ إِنَّهُمْ لَن يُغْنُوا عَنكَ مِنَ اللَّهِ شَيْئًا ۚ وَإِنَّ الظَّالِمِينَ بَعْضُهُمْ أَوْلِيَاءُ بَعْضٍ ۖ وَاللَّهُ وَلِيُّ الْمُتَّقِينَ
“Then We have put you (O Muḥammad) on a plain way of (Our) commandment [like the one which We commanded Our Messengers before you (i.e. legal ways and laws of the Islamic Monotheism)]. So follow you that (Islamic Monotheism and its laws), and follow not the desires of those who know not. [Tafsir al-Ṭabarī Vol. 25, Page 146]. Verily, they can avail you nothing against Allāh (if He wants to punish you). Verily, the Ẓālimūn (polytheists, wrong-doers, etc.) are Auliyaʾ (protectors, helpers, etc.) to one another, but Allāh is the Wali (Helper, Protector, etc.) of the Muttaqūn (pious – see V.2:2).”
[Surah Al-Jāthiyah: 45: 18-19]
The Prophet ﷺ prohibited (the acts of) treachery and betrayal and enjoined truthfulness, keeping chaste and upholding trusts. When the Messenger of Allāh ﷺ appointed anyone as the leader of an army or detachment, he would specifically advise him to fear Allāh and advise those with him from the Muslims with goodness.
The Messenger of Allāh ﷺ prohibited deceit and treason which is used by the terrorist. He ﷺ prohibited the killing of women, children, and the elderly who do not have the capability to fight (during war), he prohibited the killing those people and (spreading) corruption.
Allāh ﷻ mentioned in His noble book;
۞ وَلَا تُفْسِدُوا فِي الْأَرْضِ بَعْدَ إِصْلَاحِهَا وَادْعُوهُ خَوْفًا وَطَمَعًا ۚ إِنَّ رَحْمَتَ اللَّهِ قَرِيبٌ مِّنَ الْمُحْسِنِينَ ۞
“And do not do mischief on the earth, after it has been set in order, and invoke Him with fear and hope; Surely, Allāh’s Mercy is (ever) near unto the good-doers.” [Surat Al-Aʿrāf: 4: 56]
Allāh ﷻ informed us that He does not like the mischief makers nor does He guide the plots of the treacherous. As for what is performed today by these terrorists, who strap explosive belts around themselves or drive vehicles packed with explosives, and then find a group of people and detonate themselves (among them), this act is founded upon treachery and Islām is free from this by a great distance and it does not condone this at all!
Indeed, what is being carried out from the operations of suicide bombings in Great Britain and in other places of the various lands are nothing but the plots and actions of the Takfīrīs and Khawārij whom the Messenger of Allāh ﷺ dispraised in his statement, “There will come during the last days a young group of people, foolish who would speak the best of words. They will shoot out of Islam as the arrow shoots out of the bow. Their faith will not pass their throats. Therefore whoever finds them should kill them for indeed whoever kills them will find a reward for it on the Day of Judgement.”
Similarly it has been authentically reported that he ﷺ said about them “They are the evilest of those killed under the sky” and “The best person killed is the one who is killed by them.” And he said, “Ṭūba (a tree in paradise) is for the one who kills them and is killed by them.” And he said, “Wherever you can kill them, then kill them for there is a reward with Allāh in killing them.” Likewise he ﷺ said about them, “They are the dogs of the hell-fire” and “If I were to see them I would slaughter them like the slaughtering of ʿĀd.” And in another narration he said “the slaughtering of Thamūd.”
Likewise he ﷺ mentioned about them “They will shoot outside of the religion just as the arrow shoots out of the bow and they will not return to it until the arrow returns to from its game.” The meaning of “shoot” is to exit from the other side and the Khawārij leave the religion – meaning they leave and nothing from the religion is attached to them. Due to this, it is well known that al-Islām is free from this reckless and senseless behaviour, indeed Islām condemns its doers and disapproves such actions.
Those who accuse the Salafīs – who follow the Qurʾān and Sunnah and traverse upon the methodology of the companions, of the bombings in Britain (London 7/7) and in other places, including the killing of themselves, destroying wealth, spilling blood, scaring the public and rebelling against the government. Those who blame the Salafīs with these acts are (in reality) those who perform such wickedness. They wish to blame it on other than themselves; (and those responsible) are the people of al-Qaʿīda who follow Usāmah ibn Laden, al-Masʾari, Sād al-Faqīhī and other than them. This is because they are raised upon the books of deviant ideologies such as (the books of) Sayyid Quṭb and those who are with him upon this mistaken methodology. They are those who declare disbelief upon the Muslims without due right, but rather based upon sins which no one is saved from (committing).
In reality, it is not permissible for anyone to make takfīr except upon those whom Allāh ﷻ and his Messenger have deemed disbelievers such as the polytheist who perform major polytheism.
Allāh ﷻ said,
۞ وَلَقَدْ أُوحِيَ إِلَيْكَ وَإِلَى الَّذِينَ مِن قَبْلِكَ لَئِنْ أَشْرَكْتَ لَيَحْبَطَنَّ عَمَلُكَ وَلَتَكُونَنَّ مِنَ الْخَاسِرِينَ ۞
“And indeed it has been revealed to you (O Muḥammad), as it was to those (Allāh’s Messengers) before you: “If you join others in worship with Allāh, (then) surely (all) your deeds will be in vain, and you will certainly be among the losers.” [Surah al-Zumar: 39: 65]
He the Most High said,
۞ وَمَن يَدْعُ مَعَ اللَّهِ إِلَٰهًا آخَرَ لَا بُرْهَانَ لَهُ بِهِ فَإِنَّمَا حِسَابُهُ عِندَ رَبِّهِ ۚ إِنَّهُ لَا يُفْلِحُ الْكَافِرُونَ ۞
“And whoever invokes (or worships), besides Allāh, any other ilāh (god), of whom he has no proof, then his reckoning is only with his Lord. Surely! Al-Kāfirūn (the disbelievers in Allāh and in the Oneness of Allāh, polytheists, pagans, idolaters, etc.) will not be successful.” [Surat Al-Muʾminūn: 23: 117]
He ﷻ also said,
۞ فَلَا تَدْعُ مَعَ اللَّهِ إِلَٰهًا آخَرَ فَتَكُونَ مِنَ الْمُعَذَّبِينَ ۞
“So invoke not with Allāh another ilāh (god) lest you be among those who receive punishment.” [Surat Al-Muʾminūn: 26: 213]
And Allāh ﷻ said ʿĪsá ibn Maryam stated,
۞ يَا بَنِي إِسْرَائِيلَ اعْبُدُوا اللَّهَ رَبِّي وَرَبَّكُمْ ۖ إِنَّهُ مَن يُشْرِكْ بِاللَّهِ فَقَدْ حَرَّمَ اللَّهُ عَلَيْهِ الْجَنَّةَ وَمَأْوَاهُ النَّارُ ۖ وَمَا لِلظَّالِمِينَ مِنْ أَنصَارٍ ۞
“O Children of Israel! Worship Allāh, my Lord and your Lord.” Verily, whosoever sets up partners in worship with Allāh, then Allāh has forbidden Paradise for him, and the Fire will be his abode. And for the Ẓālimūn (polytheists and wrong-doers) there are no helpers.” [Surat Al-Māʾidah: 5: 72]
This is the truth of which is it not permissible for anyone to deviate away from and whoever claims other than this is from those people of takfīr – such as those who make takfīr on the monotheists worshippers and those who fast then he is a falsifier and a caller to falsehood. This is the truth which it is not permissible to have any doubts in and to turn away from. With Allāh lies all success.
 [TN]: This is contrary as to what befell the women, children and elderly in Mayence by the band of crusaders led by Emico. JM & MS describe the deeds of the Christian crusaders upon the Jews on their conquest of holy victory, he said “As soon as the enemy came into the courtyard they found some of the very pious there with our brilliant master, Isaac ben Moses. He stretched out his neck, and his head they cut off first. The others, wrapped by their fringed praying shawls, sat by themselves in the courtyard, eager to do the will of their Creator. They did not care to flee into the chamber to save themselves for this temporal life, but out of love they received upon themselves the sentence of God. The enemy showered stones and arrows upon them, but they did not care to flee.” The Jew in the Medieval World: A Source Book, 315-1791 By Jacob Rader Marcus, Marc Saperstein
 [TN]: To establish the judgement of disbelief upon a Muslim.