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 Sayyiduna al-Fadl, Sayyiduna Qutham, Sayyiduna Shuqran, the freed slave of the Messenger of Allah (peace and blessings be upon him), and Sayyiduna Aws bin Khawli (may Allah be pleased with them).
Hadith Referenceالمعجم الكبير للطبراني / باب الألف / 623