Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: Those who went down into the grave of the Messenger of Allah (peace and blessings be upon him) were Ali, the two sons of Abbas (may Allah be pleased with him), al-Fadl and Qutham, and Shuqran, the freed slave of the Messenger of Allah (peace and blessings be upon him) (may Allah be pleased with them). And Aws bin Khawli (may Allah be pleased with him) said to Ali (may Allah be pleased with him): O Ali! I adjure you by Allah, we too have a share in the Messenger of Allah (peace and blessings be upon him). Ali (may Allah be pleased with him) said: Come down with these people. So he too came down, and thus they were five.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11467