Musnad Ahmad 33:496

Hassan narrated to us, Ibn Lahi'ah narrated to us, Abu al-Zubayr narrated to us, he said: I asked Jabir, "Did you hear the Messenger of Allah, may Allah bless him and grant him peace, say anything regarding the abundance of a man's footsteps to the mosque?" He said: "We intended to move from our homes to [the vicinity of] the mosque, so the Messenger of Allah, may Allah bless him and grant him peace, forbade us from that. And he said: 'Do not vacate the city [of Medina], for you have a merit over those who are near the mosque: for every step, a degree.'"