Sahih al-Bukhari 4047
Narrated Khabbab bin Al-Art:
We migrated in the company of Allah's Messenger (ﷺ), seeking Allah's 
     Pleasure. So our reward became due and sure with Allah. Some of us 
     have been dead without enjoying anything of their rewards (here), and 
     one of them was Mus'ab bin 'Umar who was martyred on the day of the 
     battle of Uhud, and did not leave anything except a Namira (i.e. a 
     sheet in which he was shrouded). If we covered his head with it, his 
     feet became naked, and if we covered his feet with it, his head became
     naked. So the Prophet (ﷺ) said to us, "Cover his head with it and put some
     Idhkhir (i.e. a kind of grass) over his feet or throw Idhkhir over his
     feet." But some amongst us have got the fruits of their labor ripened,
     and they are collecting them.
حَدَّثَنَا أَحْمَدُ بْنُ يُونُسَ، حَدَّثَنَا زُهَيْرٌ، حَدَّثَنَا الأَعْمَشُ، عَنْ شَقِيقٍ، عَنْ خَبَّابٍ ـ رضى الله عنه ـ قَالَ هَاجَرْنَا مَعَ رَسُولِ اللَّهِ صلى الله عليه وسلم نَبْتَغِي وَجْهَ اللَّهِ، فَوَجَبَ أَجْرُنَا عَلَى اللَّهِ، وَمِنَّا مَنْ مَضَى أَوْ ذَهَبَ لَمْ يَأْكُلْ مِنْ أَجْرِهِ شَيْئًا، كَانَ مِنْهُمْ مُصْعَبُ بْنُ عُمَيْرٍ قُتِلَ يَوْمَ أُحُدٍ، لَمْ يَتْرُكْ إِلاَّ نَمِرَةً، كُنَّا إِذَا غَطَّيْنَا بِهَا رَأْسَهُ خَرَجَتْ رِجْلاَهُ، وَإِذَا غُطِّيَ بِهَا رِجْلاَهُ خَرَجَ رَأْسُهُ، فَقَالَ لَنَا النَّبِيُّ صلى الله عليه وسلم ‏
"‏ غَطُّوا بِهَا رَأْسَهُ، وَاجْعَلُوا عَلَى رِجْلِهِ الإِذْخِرَ ـ أَوْ قَالَ أَلْقُوا عَلَى رِجْلِهِ مِنَ الإِذْخِرِ ‏"‏‏.‏ وَمِنَّا مَنْ قَدْ أَيْنَعَتْ لَهُ ثَمَرَتُهُ فَهْوَ يَهْدُبُهَا‏.‏