Sahih Ibn Khuzaymah

Sayyiduna Abu Hurairah (may Allah be pleased with him) narrates from the Noble Prophet (peace and blessings of Allah be upon him) that he (peace be upon him) said: "When the reciter says Ameen, you should also say Ameen, because the angels also say Ameen. Therefore, whoever's Ameen coincides with the Ameen of the angels, his past sins will be forgiven."

It is narrated from Sayyiduna Abu Hurairah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "When the Imam says Ameen, then you should also say Ameen. So whoever's saying Ameen coincides with the angels' saying Ameen, his previous sins will be forgiven." Imam Abu Bakr (may Allah have mercy on him) says that in the blessed statement of the Prophet (peace and blessings be upon him), "When the Imam says Ameen, then you should also say Ameen," there is evidence and it is proven from this that the Imam will say Ameen aloud, because a person of understanding knows well that the Prophet (peace and blessings be upon him) only ordered the follower to say Ameen at the time when the Imam says Ameen, when he hears his Imam saying Ameen. And if the Imam says Ameen quietly and does not say it aloud, then the follower will not know whether his Imam has said Ameen or not, and it is impossible and inconceivable that someone should be told: When so-and-so says such-and-such, you should also say the same, even though you cannot hear his statement. This is absolutely impossible and inconceivable. Such an impossible thing cannot even occur to the mind of a knowledgeable person, that the Prophet (peace and blessings be upon him) would order the follower to say Ameen at the time when his Imam says Ameen, even though he does not hear his Imam's Ameen. Imam Abu Bakr (may Allah have mercy on him) says: Now listen to that explicit and clear hadith which is proof of the correctness of our statement, that after reciting « سورة الفاتحة », he will say Ameen aloud.

Abu Hurairah (may Allah be pleased with him) narrates that when the Messenger of Allah (peace be upon him) finished the recitation of Umm al-Qur'an, he would say "Ameen" aloud in his raised voice.

It is narrated from Hazrat Nafi' (may Allah have mercy on him) that when Sayyiduna Ibn Umar (may Allah be pleased with them both) was with the Imam and he would recite Umm al-Qur'an, the people would say Ameen, so Sayyiduna Umar (may Allah be pleased with him) would also say Ameen, and he considered it a Sunnah.

It is narrated from Sayyiduna Bilal (may Allah be pleased with him) that he submitted to the Noble Prophet (peace and blessings be upon him), "Do not precede me in saying Ameen." Imam Abu Bakr (may Allah have mercy on him) says that Muhammad bin Hassan narrated this hadith to us exactly in this way: that Imam Sufyan Thawri narrates from his teacher Asim, and he from Sayyiduna Bilal (may Allah be pleased with him), whereas other narrators in this chain add the teacher of Asim, Abu Uthman (and he says that) « ان بلا لا قال للنبي صلى الله عليه وسلم » "Sayyiduna Bilal (may Allah be pleased with him) submitted to the Noble Prophet (peace and blessings be upon him)."