Sahih al-Bukhari 340
Narrated `Abdur Rahman bin Abza:
that while he was in the company of `Umar, `Ammar said to `Umar, "We were in a detachment and 
became Junub and I blew the dust off my hands (performed the rolling over the earth and prayed.)"
حَدَّثَنَا سُلَيْمَانُ بْنُ حَرْبٍ، قَالَ حَدَّثَنَا شُعْبَةُ، عَنِ الْحَكَمِ، عَنْ ذَرٍّ، عَنِ ابْنِ عَبْدِ الرَّحْمَنِ بْنِ أَبْزَى، عَنْ أَبِيهِ، أَنَّهُ شَهِدَ عُمَرَ وَقَالَ لَهُ عَمَّارٌ كُنَّا فِي سَرِيَّةٍ فَأَجْنَبْنَا، وَقَالَ تَفَلَ فِيهِمَا‏.‏