Sayyiduna Khabbab bin al-Aratt (may Allah be pleased with him) said: We emigrated with the Messenger of Allah (peace and blessings be upon him) in the path of Allah, seeking the pleasure of Allah Almighty, and our reward became due upon Allah. Among us were those who passed on without enjoying anything of that reward; one of them was Mus'ab bin Umayr (may Allah be pleased with him), who was martyred on the day of Uhud. We found nothing in which to shroud him except a coarse woollen sheet (namirah); when we placed it over his face, that is, over his head, his feet came out, and when we put it over his feet, his head was left bare. The Messenger of Allah (peace and blessings be upon him) said: "Put it over his head, and put idhkhir grass over his feet." Then he said: And among us are those whose fruit has ripened and who are picking it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6682