Mishkat al-Masabih #654

He also reported God’s Messenger as saying, “A man's prayer in company is twenty-five times as valuable as his prayer in his house and his market, for when he performs ablution, doing it well, then goes out to the mosque, having no other reason than prayer for going out, he does not take a step without being raised a degree for it and having a sin remitted for it, and when he prays the angels continue to invoke blessings on him as long as he is in his place of prayer, saying, ‘God bless him; God show mercy to him.’ And each of you continues to be engaged in prayer as long as he is waiting for the prayer.” In a version he said, “When he enters the mosque prayer holds him fast.” And he added in the invocation of the angels, “O God, forgive him, O God, turn towards him, as long as he does not do any harm in it and as long as he does not do anything unseemly in it.” (Bukhari and Muslim.)