It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "When one of you walks with a funeral, he should not sit until it is placed on the ground."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6876