Maliks Muwatta Book 19, Hadith Number 5.

Yahya related to me that Ziyad ibn Abd ar-Rahman said, “Malik related to us from Sumayy, the mawla of Abu Bakr ibn Abd ar-Rahman, that Abu Bakr ibn Abd ar-Rahman was once doing itikaf and he would go out to relieve himself in a closed room under a roofed passage in Khalid ibn Walid’s house. Otherwise he did not leave his place of itikaf until he went to pray at the Id with the muslims.”