Praise be to Allah, and may peace and blessings be upon the Messenger of Allah.
The word “forgetting” in Arabic has two meanings:
An example of “forgetting” in the sense of abandoning is Allah’s saying:
﴿They forgot Allah, so He forgot them﴾ [At-Tawbah 9:67].
That is, they abandoned obedience to Allah and turned away from His commands, so Allah recompensed them by leaving them deprived of His mercy and guidance.
Forgetting in the sense of being unaware, heedless, or failing to remember something cannot be attributed to Allah, because it is a deficiency and imperfection, while Allah is far above every deficiency.
Allah تعالى says:
﴿He said: “Its knowledge is with my Lord in a Record. My Lord neither errs nor forgets.”﴾ [Ta-Ha 20:52].
Allah تعالى is never unaware of anything, does not forget anything within His knowledge, and nothing in the heavens or on earth escapes Him.
As for the “forgetting” mentioned in some texts regarding Allah تعالى, it does not mean heedlessness or loss of awareness. Rather, it means abandonment, turning away, and recompense according to the nature of the deed.
Allah تعالى says:
﴿So taste [the punishment] because you forgot the meeting of this Day. Indeed, We have forgotten you.﴾ [As-Sajdah 32:14].
And He سبحانه says:
﴿They forgot Allah, so He forgot them.﴾ [At-Tawbah 9:67].
The meaning is that these people abandoned Allah’s commands and turned away from obedience to Him, so they were recompensed by being left without mercy and guidance, and by being turned away from in the context of recompense.
Ibn Kathir رحمه الله said in his commentary on Allah’s saying:
﴿So today We will forget them just as they forgot the meeting of this Day﴾:
Allah تعالى treats them as one who has forgotten them, although nothing is absent from His knowledge and He does not forget anything. Rather, this expression is used by way of reciprocity and recompense.
Shaykh Salih Al-Fawzan حفظه الله stated that the forgetting negated from Allah is that which means heedlessness and loss of awareness. As for the forgetting affirmed in verses such as ﴿They forgot Allah, so He forgot them﴾, it means that He left them in misguidance and turned away from them as a recompense for abandoning His commands and turning away from His religion.
Based on the above, a person saying to his friend:
“Do not forget Allah, lest He forget you”
is correct in meaning, and there is nothing wrong with using this expression.
The meaning of “Do not forget Allah” is: Do not neglect Allah’s commands, and do not abandon obedience to Him and remembrance of Him.
The meaning of “lest He forget you” is: Allah may leave you without His guidance and mercy and recompense you according to the nature of your deeds, as He سبحانه says:
﴿They forgot Allah, so He forgot them.﴾
It does not mean that Allah تعالى might become heedless of His servant or forget him in the sense of being unaware or lacking knowledge. Exalted is Allah far above that. Rather, it means abandonment and turning away from mercy and guidance as a form of recompense.
The expression “Do not forget Allah, lest He forget you” is permissible in meaning and is consistent with what is stated in the Noble Qur’an.
Its meaning is: Do not abandon obedience to Allah and His commands, and do not neglect His rights, lest Allah recompense you by leaving you and turning away from you, thereby depriving you of His mercy and guidance.
As for attributing forgetting to Allah تعالى in the sense of heedlessness or loss of awareness, this is impermissible, because Allah سبحانه “neither errs nor forgets.”
And Allah تعالى knows best.