Musnad Abu Ya'la al-Mawsili 159:2

Zuhayr ibn Harb narrated to us, Sufyan ibn 'Uyaynah narrated to us, from al-Zuhri, from al-A'raj, from Abu Hurayrah, from the Prophet, peace and blessings of Allah be upon him, who said: "If one of you asks his neighbor for permission to insert a piece of wood into his wall, he should not prevent him."