Mukhtasar Bukhari (Abridged) 449 — Virtue of saying Ameen

Narrated from Sayyiduna Abu Huraira (may Allah be pleased with him) that the Messenger of Allah (peace and blessings of Allah be upon him) said: "When any one of you says Ameen and the angels in the heavens say (Ameen), and these two coincide with each other, then his previous sins are forgiven."