Sahih Muslim
The Book of Prayers (Kitab Al-Salat)
Book Number: 004 / Hadith Number: 1401
Abu Musa reported Allah's Messenger (may peace be upon him) as saying: The most eminent among human beings (as a recipient of) reward (is one) who lives farthest away, and who has to walk the farthest distance, and he who waits for the prayer to observe it along with the Imam, his reward is greater than one who prays (alone) and then goes to sleep. In the narration of Abu Kuraib (the words are):" (He waits) till he prays along with the Imam in congregation."