Musnad Ahmad 761:0

Narrated to us by Abu al-Mughirah, who said: Narrated to us Safwan, who said: Narrated to us Shurayh ibn Ubayd, from Abu Ruhm al-Ghifari, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever performs Wudu (ablution) and performs it well, then walks to the prayer, and prays with the people—or he said: with the congregation—or in the mosque, Allah will forgive his sins." He said: So I said to him: "O Abu Ruhm, what if he does not find a place in the mosque?" He said: "If he performs Wudu well, then goes out intending nothing but the prayer, he will not take a step except that Allah will raise him a degree by it, and erase a sin from him, until he enters the mosque. If he enters the mosque, he is in prayer as long as he is waiting for the prayer."