Musnad Ahmad 482:164

Yahya ibn Ishaq narrated to us, Ibn Lahi'ah informed us, from a sheikh from Ma'afir, who said: I heard Uqbah ibn Amir al-Juhani saying: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "When a man performs ablution, then comes to the mosque, Allah writes for him ten good deeds for every step he takes. And when he prays in the mosque, then sits in it, he is like the fasting one who stands in prayer until he returns."