عَنْ عَلِيٍّ وَمُعَاذِ بْنِ جَبَلٍ رَضِيَ اللَّهُ عَنْهُمَا قَالَا: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «إِذَا أَتَى أَحَدُكُمْ الصَّلَاةَ وَالْإِمَامُ عَلَى حَالٍ فَلْيَصْنَعْ كَمَا يَصْنَعُ الْإِمَامُ» . رَوَاهُ التِّرْمِذِيُّ وَقَالَ: هَذَا حَدِيثٌ غَرِيبٌ

Abu Sa'id al-Khudri told how a man came when God’s Messenger had already prayed, and he said, “Will no one give alms* to this man and pray along with him?” Thereupon a man got up and prayed along with him. * This is a literal translation. The idea is that by joining with him he increased the reward the man would receive for his prayer, as prayer in company has a much greater reward than prayer alone.Tirmidhi and Abu Dawud transmitted it.