Musannaf Ibn Abi Shayba 6:869

Khalaf ibn Khalifah narrated to us, from his father—I think he heard it from Ma'qil—from the Prophet, may Allah bless him and grant him peace, that he lowered Nu'aym ibn Mas'ud al-Ashja'i into the grave and removed the *akhillah* (the wooden slats/pegs) with his mouth. The remainder means the knots.