Sahih Bukhari Volume 1, Book 7, Hadith 338

حَدَّثَنَا آدَمُ، قَالَ حَدَّثَنَا شُعْبَةُ، حَدَّثَنَا الْحَكَمُ، عَنْ ذَرٍّ، عَنْ سَعِيدِ بْنِ عَبْدِ الرَّحْمَنِ بْنِ أَبْزَى، عَنْ أَبِيهِ، قَالَ جَاءَ رَجُلٌ إِلَى عُمَرَ بْنِ الْخَطَّابِ فَقَالَ إِنِّي أَجْنَبْتُ فَلَمْ أُصِبِ الْمَاءَ‏.‏ فَقَالَ عَمَّارُ بْنُ يَاسِرٍ لِعُمَرَ بْنِ الْخَطَّابِ أَمَا تَذْكُرُ أَنَّا كُنَّا فِي سَفَرٍ أَنَا وَأَنْتَ فَأَمَّا أَنْتَ فَلَمْ تُصَلِّ، وَأَمَّا أَنَا فَتَمَعَّكْتُ فَصَلَّيْتُ، فَذَكَرْتُ لِلنَّبِيِّ صلى الله عليه وسلم فَقَالَ النَّبِيُّ صلى الله عليه وسلم ‏"‏ إِنَّمَا كَانَ يَكْفِيكَ هَكَذَا ‏"‏‏.‏ فَضَرَبَ النَّبِيُّ صلى الله عليه وسلم بِكَفَّيْهِ الأَرْضَ، وَنَفَخَ فِيهِمَا ثُمَّ مَسَحَ بِهِمَا وَجْهَهُ وَكَفَّيْهِ‏

Narrated By 'Abdur Rahman bin Abza : A man came to 'Umar bin Al-Khattab and said, "I became Junub but no water was available." 'Ammar bin Yasir said to 'Umar, "Do you remember that you and I (became Junub while both of us) were together on a journey and you didn't pray but I rolled myself on the ground and prayed? I informed the Prophet about it and he said, 'It would have been sufficient for you to do like this.' The Prophet then stroked lightly the earth with his hands and then blew off the dust and passed his hands over his face and hands.