Sahih Bukhari
Merits of the Helpers in Madinah (Ansaar)
Volume: 005 / Book Number: 058 / Hadith Number: 237
Narrated Abu Wail:
We visited Khabbaba who said, "We migrated with the Prophet for Allah's Sake, so our reward became due and sure with Allah. Some of us passed away without taking anything of their rewards (in this world) and one of them was Mus'ab bin 'Umar who was martyred on the day (of the battle) of Uhud leaving a striped woolen cloak. When we covered his head with it, his feet became naked, and when covered his feet, his head became naked.
So Allah's Apostle ordered us to cover his head and put some Idhkhir (i.e. a special kind of grass) on his feet. (On the other hand) some of us have had their fruits ripened (in this world) and they are collecting them."