Musnad Ahmad 937:17

Muhammad ibn Ja‘far narrated to us, Shu‘bah narrated to us, from Ayyub, from Abu Qilabah, from a man from Banu Qushayr, who said: I used to be away from water, and major ritual impurity (janabah) would befall me, and I would not find water, so I would perform tayammum. That caused doubt in my soul, so I went to Abu Dharr at his house, but I did not find him. Then I went to the mosque, and his appearance had been described to me, and there he was, praying, so I recognized him by the description. I greeted him, but he did not return the greeting until he finished, then he returned the greeting to me. I said: "Are you Abu Dharr?" He said: "My family claims that." I said: "There was no one among the people whose sight was more beloved to me than you." He said: "You have seen me." I said: "I used to be away from water, and major ritual impurity would befall me, and I would remain for days performing tayammum, and that caused doubt in my soul," or he said, "It became confusing to me." He said: "Do you know Abu Dharr? I was in Medina and I found it unhealthy, so the Messenger of Allah (peace and blessings of Allah be upon him) ordered a small flock of sheep for me, and I went out with them. Major ritual impurity befell me, so I performed tayammum with the soil and prayed for days. That caused doubt in my soul until I thought I was perishing. So I ordered a she-camel of mine, or a young camel, and it was saddled, then I mounted it and came until I arrived in Medina. I found the Messenger of Allah (peace and blessings of Allah be upon him) in the shade of the mosque among a group of his companions. I greeted him, and he raised his head and said: 'Subhan Allah, Abu Dharr?'" I said: "Yes, O Messenger of Allah. Major ritual impurity befell me, so I performed tayammum for days, and that caused doubt in my soul until I thought I was perishing." The Messenger of Allah (peace and blessings of Allah be upon him) called for water for me, and a black slave girl brought it in a wooden bowl, splashing. I hid behind the riding beast, and the Messenger of Allah (peace and blessings of Allah be upon him) ordered a man to screen me, so I performed ghusl. Then the Messenger of Allah (peace and blessings of Allah be upon him) said: "O Abu Dharr, the pure soil is a purifier, even if you do not find water for ten years. But if you find water, then let it touch your skin."