Musnad Ahmad 28:20

Sufyan narrated to us, from Dawud—meaning Ibn Shabur—from Mujahid, and Bashir Abu Isma'il, from Mujahid, from Abdullah ibn Amr ibn al-Aas, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Gabriel kept enjoining upon me [to treat] the neighbor well, until I thought that he would make him an heir."