Musnad Ahmad 32:1826

Abdullah ibn Bakr narrated to us, Humaid narrated to us, from Anas, who said: The Banu Salama wanted to move from their dwellings to near the mosque. The Prophet of Allah, may Allah bless him and grant him peace, disliked that the outskirts of Medina should be left vacant. So he said: "O Banu Salama, will you not seek the reward for your footsteps?"