This is a controversial issue, and the majority opinion is that saying ʼAāmīn out loud in audible prayer is permissible for everyone, whether the Imam, the follower, or the one praying audibly alone. They base their argument on the Ḥadīths and narrations that have been reported on this matter. For example, Abū Hurayrah (may Allāh be pleased with him) narrated that the Prophet (peace be upon him) said: “When the Imam says (ʼAāmīn), then say (ʼAāmīn), for whoever’s saying of ʼAāmīn coincides with the saying of the angels, his past sins will be forgiven.” This Ḥadīth is agreed upon by Al-Bukhāriy and Muslim. Moreover, there is the Ḥadīth of Wāʼil ibn Ḥajar, who said that when the Prophet (peace be upon him) recited {not (the way) of those who earned Your Anger, nor of those who went astray}, he said (ʼAāmīn) and raised his voice. This Ḥadīth was reported by Abū Dawūd.
Imam Mālik, on the other hand, in one narration reported on his authority, believes that it is a Sunnah (recommended) to say ʼAāmīn audibly for the follower, but not for the Imam. He used as evidence what he narrated from Abū Hurayrah that when the Imam says {not (the way) of those who earned Your Anger, nor of those who went astray}, then you say (ʼAāmīn). This Ḥadīth was reported by Imam Mālik, which indicates that the Imam does not say it out loud. However, the Ḥanafiys and Imam Mālik, in the other narration reported on his authority, believe that it is a Sunnah to say ʼAāmīn silently because it is a supplication, and we recite supplications in prayer silently, such as the supplication of prostration, Tashahhud, and Tasbīḥ.
Hence, everyone should say ʼAāmīn, but the disagreement occurs in whether saying it audibly or silently.
Regarding the second part of the question, which is about some people rush to say ʼAāmīn before the Imam, it is also a point of disagreement among the scholars. The point of disagreement is whether we should start saying ʼAāmīn after the Imam finishes reciting {not (the way) of those who earned Your Anger, nor of those who went astray}, or should we start saying it when the Imam says ʼAāmīn, or should we wait until the Imam finishes saying ʼAāmīn for himself, then we say it afterward?
This is the point of disagreement. If we look at the Ḥadīths, we find that they have been reported in multiple forms, including the evidence of the first opinion of the first part of the question, which is to say ʼAāmīn after the Imam finishes reciting {not (the way) of those who earned Your Anger, nor of those who went astray}. Abū Hurayrah (may Allāh be pleased with him) narrated that the Prophet (peace be upon him) said: “When the Imam says {not (the way) of those who earned Your Anger, nor of those who went astray}, then you say (ʼAāmīn,) for whoever’s saying coincides with the saying of the angels, his past sins will be forgiven.” This indicates that saying ʼAīmīn comes after the end of the recitation.
The evidence of the second opinion is to say ʼAāmīn while the Imam is saying it, as indicated by the Prophet’s (peace be upon him) statement: “When the Imam says (ʼAāmīn), then you say (ʼAāmīn), for whoever’s saying of ʼAāmīn coincides with the saying of the angels, his past sins will be forgiven.” This Ḥadīth is agreed upon by Al-Bukhāriy and Muslim. This refers to saying it while the Imam is saying it.
The evidence of the third opinion is to delay saying ʼAāmīn until the Imam says it, as narrated by Abū Hurayrah, who led the people in prayer and recited {In the name of Allah, the Most Gracious, the Most Merciful}, then recited Sūrat Al-Fātiḥah, until he reached {not (the way) of those who earned Your Anger, nor of those who went astray}, then said ʼAāmīn. Afterwards, the people also said ʼAāmīn. He (Abū Hurayrah) would say “Allāhu ʼAkbar” whenever he moved to prostration and when he moved to stand up after the sitting position in the second Rakʽah. When he finished the prayer, he said: “By the One in Whose Hand is my soul, I prayed a prayer similar to the prayer of the Messenger of Allāh (peace be upon him).” This refers to saying ʼAāmīn after the Imam says it not while he is saying it.
Therefore, we can confirm that the agreed-upon part is to avoid rushing to say ʼAāmīn ahead of the Imam, while saying it in coincidence with the Imam, following him or delaying it after the recitation of {not (the way) of those who earned Your Anger, nor of those who went astray} are all valid.
After all, Allāh knows best.
Fatwa by Dr. Khālid Naṣr