Muwatta Imam Malik Book of Jihad, Hadith 37

Yahya related to me from Malik that he had heard the people of knowledge say that martyrs in the way of Allah were not washed, nor were any of them prayed over. They were buried in the garments in which they were slain.
Malik said, "That is the sunna for someone who is killed on the battleground and is not reached until he is already dead. Someone who is carried off and lives for as long as Allah wills after it, is washed and prayed over as was Umar ibn al- Khattab."

وَحَدَّثَنِي عَنْ مَالِكٍ أَنَّهُ بَلَغَهُ عَنْ أَهْلِ الْعِلْمِ أَنَّهُمْ كَانُوا يَقُولُونَ الشُّهَدَاءُ فِي سَبِيلِ اللَّهِ لاَ يُغَسَّلُونَ وَلاَ يُصَلَّى عَلَى أَحَدٍ مِنْهُمْ وَإِنَّهُمْ يُدْفَنُونَ فِي الثِّيَابِ الَّتِي قُتِلُوا فِيهَا . قَالَ مَالِكٌ وَتِلْكَ السُّنَّةُ فِيمَنْ قُتِلَ فِي الْمُعْتَرَكِ فَلَمْ يُدْرَكْ حَتَّى مَاتَ . قَالَ وَأَمَّا مَنْ حُمِلَ مِنْهُمْ فَعَاشَ مَا شَاءَ اللَّهُ بَعْدَ ذَلِكَ فَإِنَّهُ يُغَسَّلُ وَيُصَلَّى عَلَيْهِ كَمَا عُمِلَ بِعُمَرَ بْنِ الْخَطَّابِ .