كتاب الصلاة
4  
Prayer
(29b)
Chapter: The manner in which one who is led in prayer by an Imam must follow him, and the rule applying to the one who is preceded by him - Section 2
(28)
باب ما على المأموم من المتابعة وحكم المسبوق - الفصل الثاني
Mishkat al-Masabih 1146
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.
وَعَن أبي سعيد الْخُدْرِيّ قَالَ: جَاءَ رَجُلٌ وَقَدْ صَلَّى رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فَقَالَ: «أَلَا رَجُلٌ يَتَصَدَّقُ عَلَى هَذَا فَيُصَلِّيَ مَعَهُ؟» فَقَامَ رَجُلٌ فيصلى مَعَه ". رَوَاهُ التِّرْمِذِيّ وَأَبُو دَاوُد
  صَحِيح   (الألباني) حكم   :
Reference : Mishkat al-Masabih 1146
In-book reference : Book 4, Hadith 563