Musannaf Ibn Abi Shayba 36:496

Waki’ narrated to us, from Isma’il bin Abi Khalid, from ‘Amir, who said: ‘Ali, al-Fadl, and Usama entered the grave of the Prophet, may Allah bless him and grant him peace. Al-Sha’bi said: And Marhab, or the son of Abi Marhab, narrated to me that ‘Abd al-Rahman bin ‘Awf entered the grave with them.