Sahih Muslim Book 4, Hadith Number 880.

Chapter : The command to observe prayer with tranquillity and calmness and forbiddance of making gesture with hands and lifting them while pronouncing salutation, and the completing of first rows and joining together well in them.

Abu Huraira reported: The Messenger of Allah (may peace be upon him) said: If you were to know, or if they were to know, what (excellence) lies in the first rows, there would have been drawing of lots (for filling them); and Ibn Harb said: For (occupying) the first row there would have been drawing of lots.