The Messenger of Allah (ﷺ) said: "If any one of you says: 'Amin' and the angels in Heaven say Amin, and the one coincides with the other, his previous sins will be forgiven."
Sunan an-Nasa'i Book 11, Hadith 55
← Previous Hadith The Messenger of Allah (ﷺ) said: "When the Imam says: Not (the way) of those who earned Your anger, nor of those who went astray, say: 'Amin,' for if a person's Amin coincides with the Amin of the angels, his previous sins will be forgiven.'"

Sunan an-Nasa'i Book 11, Hadith 54 Next Hadith → His father said: "I prayed behind the Prophet (ﷺ) and I sneezed and said: 'Al-hamdu lillahi, hamdan kathiran tayiban mubarakan fih, mubarakan'alaihi, kama yuhibbu rabbuna wa yarda (Praise be to Allah, much good and blessed praise as our Lord loves and is pleased with.)' When he finished praying, the Messenger of Allah (ﷺ) said: 'Who is the one who spoke during the prayer?' But no one said anything. Then he said it a second time: 'Who is the one who spoke during the prayer?' So Rifa'ah bin Rafi bin Afrah said: 'It was me, O Messenger of Allah.' He said: 'I said: "Praise be to Allah, much good and blessed praise as our Lord loves and is pleased with.'" The Prophet (ﷺ) said: 'By the One in Whose hand is my soul, thirty-odd angels hastened to see which of them would take it up.'"

Sunan an-Nasa'i Book 11, Hadith 56