“Does a person in a state of ignorance (today) say “Allāh and His Messenger know best” and is this (only) said regarding matters of the religion or can it (also be) said regarding worldly affairs?”

Shaykh Ṣāliḥ ibn Fawzān al-Fawzān:

“This used to be said when the Messenger ﷺ was alive. It would be said “Allāh and his Messenger know best.” When the Messenger ﷺ died, it was then said: “Allāh knows best.”

(He should) say “Allāh knows best” in everything which he doesn’t know, whether in the matters of the religion or worldly. Everything he doesn’t know then he should say: “Allāh knows best.”