Praise be to Allah, and may peace and blessings be upon the Messenger of Allah. To proceed:
There is no harm in supplicating by saying: “O Allah, be a protector, supporter, and trustee for the Muslims.” The meaning of “Amin” here is correct, as in Arabic usage it can mean protector, watcher, and guardian, and these are meanings established for Allah تعالى. However, “Al-Amin” is not one of the established Beautiful Names of Allah in an unrestricted sense. Rather, it is permissible to use this expression when speaking about Allah تعالى if the correct meaning is intended. Nevertheless, it is preferable to avoid this expression in supplication if it causes confusion or objections among the worshippers, especially since this supplication is not among the supplications transmitted from the Prophet صلى الله عليه وسلم.
Allah تعالى says:
﴿He is Allah, other than whom there is no deity: the King, the Most Holy, the Source of Peace, the Granter of Security, the Guardian﴾ [Al-Hashr: 23].
The scholars have mentioned that among the meanings of “Al-Muhaymin” (the Guardian) are: the trustworthy, the watcher, the protector, and the witness over His creation.
Al-Bayhaqi, may Allah have mercy on him, said:
“Al-Muhaymin is the witness over His creation concerning what proceeds from them of speech or action... It has also been said: He is the trustworthy; and it has been said: He is the watcher over something and its protector.”
Ibn Atiyyah, may Allah have mercy on him, said:
“Al-Muhaymin means: the trustworthy and the protector.”
Accordingly, using the expression “Amin” in this supplication, when what is intended is the protector, watcher, and guardian over His creation, has a correct meaning and does not imply any deficiency regarding Allah تعالى.
A distinction should be made between a Divine Name and speaking about Allah تعالى using a particular expression.
“Al-Amin” is not among the Beautiful Names of Allah that have been established—in this particular form—in the revealed texts in a manner that makes it one of the Names through which Allah is worshipped and invoked on the basis of revealed specification.
However, it is permissible to speak about Allah تعالى using an expression that has a correct meaning when its meaning is established by the Qur’an and Sunnah and it does not imply any deficiency or false meaning.
Therefore, the permissibility of saying “Allah is Amin”, meaning the Protector and Watcher, does not necessarily mean that “Al-Amin” is one of Allah’s Beautiful Names.
In terms of meaning, supplicating by saying: “O Allah, be a protector, supporter, and trustee for the Muslims” is permissible, and there is no harm in it if “Amin” is intended to mean the protector and watcher.
However, an important point should be noted: this expression is not among the supplications transmitted from the Prophet صلى الله عليه وسلم.
Therefore, if using it leads to confusion or misunderstanding among some worshippers, it is preferable for the imam to supplicate using clear, transmitted expressions, or supplications whose meanings are sound and which do not cause people difficulty or disagreement.
The fact that a supplication is permissible in meaning does not mean that it is preferable to the prophetic supplications that have been transmitted.
Yes, the imam’s decision to stop using this expression when confusion arose among the worshippers was appropriate, because the purpose of supplication is to ask Allah تعالى for goodness, not to adhere to wording that may cause confusion when there are transmitted and permissible supplications that can serve the same purpose.
This does not mean that the original expression was prohibited. Rather, abandoning it was a matter of choosing what is clearer and farther removed from ambiguity.
It is permissible for a Muslim to say: “O Allah, be a protector, supporter, and trustee for the Muslims,” if by “Amin” he means the protector, watcher, and guardian, because this meaning is correct regarding Allah تعالى.
However, “Al-Amin” is not an unrestrictedly established Name of Allah in this form. Therefore, the permissibility of speaking about Allah using this expression does not mean that it is one of His Beautiful Names.
Although the supplication is permissible in meaning, when there is confusion or objection, it is preferable to use transmitted supplications or clear expressions, especially since this wording is not among the prophetic supplications that have been transmitted.
And Allah تعالى knows best.