These are the occasions in which initiating the Islamic greeting is disliked;
1. The One Speaking: It is disliked to initiate the Islamic greeting to a person who is speaking since he is busy with conversing with someone.
2. The One Busy with Remembering Allah: “The one who is occupied with remembering Allāh ﷻ” meaning saying – SubḥānAllāh, Allāhu Akbar and reciting the Quʾān.
3. The One Busy with the Speech of Muḥammad: Meaning the one who is busy in [reading, studying and memorising] the ḥadīth of the Prophet ﷺ.
4. The Orator: Meaning to greet the khaṭīb at times other than the Friday sermon, since speaking in Friday prayer is [already] prohibited, it is prohibited to greet the khāṭīb and those listening.
5. The One Teaching: “…whilst teaching…” meaning the person who is engaged in teaching the Qurʾān, ḥadīth, matters of jurisprudence or Arabic grammar, do not greet him. Some people, when they arrive to a gathering whilst the lesson has commenced, they greet and raise their voices. This is disliked since this will distract the teacher and those sitting and listening. This would cause the people to turn their attention to him (rather than the teacher).
6. The One Researching Knowledge: “..who is indulged in researching the sciences of knowledge..” meaning the person who is researching an academic issue. Do not greet him and disturb his research. This is not correct.
7. The Preacher: “..or the preacher..” meaning the one preaching to the people, so do not greet him if you arrive. Sit down and listen to the admonition and do not extend the Islamic greetings as you will disturb the lecturer and those listening.
8. The faqīḥ: Meaning the one revising knowledge of jurisprudence (fiqḥ).
9. The Caller to the Prayer: [meaning] the one calling the ʾathān for the prayer. Do not greet him whilst he is calling the people to prayer since you will disturb him during the ʾathān.
10. The One Praying: “..the one in prayer..” meaning if you arrive and there is a person praying then do not greet him until he has completed his prayer. It has been reported from the Prophet ﷺ that one of the companions had greeted him and he returned the salutation by indicating [with his hand, head or finger]. So if someone greets you whilst you are in prayer then return the salutation by indication.
11. The One Purifying Himself: “..or a person purifying himself..” the one who is performing the ablution, so do not greet him until he has finished making his ablution. However, if he is washing himself for other than the purpose of worship such as cooling down or merely cleaning, then there is no problem for you to greet him.
12. The One Eating: It is not legislated to greet the one busy eating.
13. The One Reliving Himself: “..and he who is relieving himself..” And this is severe. This is referring to the person who is urinating or defecating; do not greet him whilst he is relieving himself. Since it is disliked for the one urinating or defecating to speak whilst in this condition, so do not greet him.
14. The Mujāhid: “..the person who is engaged in fighting the enemy in jiḥād.” the last occasion is the fighter who is engaged in battle, do not greet him whilst he is fighting, because he is engaged in fighting the enemy of Allāh ﷻ.