Abu Ishaq (may Allah have mercy on him) says that al-Harith left a will that Sayyiduna Abdullah bin Yazid (may Allah be pleased with him) should lead his funeral prayer. Then he was placed into the grave from the foot end, and he said: "This is the Sunnah."
This chain is sahih (authentic). Since he said 'This is from the Sunnah', it has become like a musnad (Prophetic) report. We have also narrated this statement from Ibn Umar and Anas bin Malik.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 7052