This view is narrated from Alqamah, al-Aswad, Suwayd bin Ghafalah, Ata, Tawus, Mujahid, Salim, al-Qasim and al-Hasan al-Basri (may Allah have mercy on them); they said: "The imam (ruler) will step forward (to lead the funeral prayer)."
It is also narrated from Sayyiduna Ali (peace be upon him) and Sayyiduna Jarir bin Abdullah (may Allah be pleased with him), but it is not established from either of them; however, it is well known from Sayyiduna al-Husayn bin Ali (may Allah be pleased with him).
Abu Hazim said: I was present on the day al-Hasan bin Ali (may Allah be pleased with him) died. I saw al-Husayn bin Ali (may Allah be pleased with him) saying to Sa'id bin al-As: "Step forward; were it not the Sunnah, you would not have been put forward." And he was jabbing him in the neck, for there was some discord between them. Then Abu Hurayrah (may Allah be pleased with him) said: "Do you begrudge the son of your Prophet a patch of earth in which you will bury him? While I heard the Messenger of Allah (peace and blessings be upon him) say: 'Whoever loves these two has loved me, and whoever hates them has hated me.'"
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6894