Musnad Ahmad 759:7

Abdullah ibn Ahmad said: Harun ibn Ma'ruf, Abu Ma'mar, and Muhammad ibn Hassan al-Samti narrated to us, they said: Ali ibn 'Abis narrated to us, from Abu Fazara, from Abd al-Rahman ibn Abi Layla, from his father, who said: "I saw the Prophet, may Allah bless him and grant him peace, performing i'tikaf in a dome made of palm leaves."