We were with Umar when a man came to him and said, "Commander of the Believers, we sometimes remain a month or two without finding water."Umar replied, "As for me, I would not pray until I found water."Ammar then said, "Commander of the Believers, do you remember when we were at such-and-such a place tending camels, and you know that we became junub?"Umar said, "Yes."Ammar continued, "I rolled in the dust, then came to the Prophet ﷺ and told him what I had done. He laughed and said, 'Clean earth would have been enough for you,' and he struck the ground with his palms, blew on them, then wiped his face and part of his forearms with them."Umar said, "Fear Allah, Ammar."Ammar replied, "Commander of the Believers, if you wish, I will not mention it for as long as I live."Umar said, "No, by Allah, but we leave you to bear the responsibility for what you have taken upon yourself."
حدثنا عبد الرحمن بن مهدي حدثنا سفيان عن سلمة يعني ابن كهيل عن أبي مالك وعبد الله بن عبد الرحمن بن أبزى
كنا عند عمر فأتاه رجل فقال يا أمير المؤمنين إنا نمكث الشهر والشهرين لا نجد الماء فقال عمر أما أنا فلم أكن لأصلي حتى أجد الماء فقال عمار يا أمير المؤمنين تذكر حيث كنا بمكان كذا ونحن نرعى الإبل فتعلم أنا أجنبنا قال نعم قال فإني تمرغت في التراب فأتيت النبي ﷺ فحدثته فضحك وقال كان الصعيد الطيب كافيك وضرب بكفيه الأرض ثم نفخ فيهما ثم مسح بهما وجهه وبعض ذراعيه قال اتق الله يا عمار قال يا أمير المؤمنين إن شئت لم أذكره ما عشت أو ما حييت قال كلا والله ولكن نوليك من ذلك ما توليت
Its isnad is sahih, mentioned previously at 18250 and its cross-references.