Sahih Bukhari Volume 001, Book 011, Hadith Number 628.
Narated By Abu Huraira : Allah's Apostle said, "The angels keep on asking for Allah's Blessing and Forgiveness for anyone of you as long as he is at his Musalla (praying place) and does not do Hadath (passes wind). The angels say, 'O Allah! Forgive him and be Merciful to him.' Each one of you is in the prayer as long as he is waiting for the prayer and nothing but the prayer detains him from going to his family."