—for the Messenger of Allah ﷺ said, “The wholesome earth is a purifier for the Muslim even if he has no water for ten years. Yet when he does find water, let him make it touch his skin, for that is better.” (Abū Dāwūd, al-Tirmidhī—sound; also Aḥmad—from Abū Dharr).

There is supporting evidence from a report of Abū Hurayrah with a sound chain, as Ibn al-Qaṭṭān affirmed. I add: its transmitters are the same men found in al-Bukhārī’s collection, with the wording, “Let him fear Allah and let the water touch his skin.” See al-Zaylaʿī (1/148-150). This is likewise the opinion of Ibn al-Musayyib, al-Ḥasan al-Baṣrī, al-Zuhrī, Abū Jaʿfar al-Bāqir, and Yazīd ibn Hārūn (al-Muḥallā 2/128).

When water does become available, he is not obliged to repeat the prayers he has already performed; this is the doctrine of the four Imams. Abū Saʿīd related: “Two men set out on a journey. The time for prayer arrived but they had no water, so they performed tayammum with clean earth and prayed. They then found water while the prayer time remained. One of them repeated his ablution and the prayer, while the other did not. When they came to the Messenger of Allah ﷺ and informed him, he said to the one who had not repeated, ‘You have adhered to the sunnah, and your prayer is sufficient,’ and to the one who had repeated, ‘You will have a double reward.’” (Abū Dāwūd, al-Nasāʾī and others; see Naqd al-Tāj).

A dry ablution is nullified only by whatever breaks wudu or by the subsequent discovery of water, as shown by the aforementioned hadiths of Abū Dharr and Abū Hurayrah, and by his ﷺ statement—in the report about the man who stayed away from the prayer because he was junub, mentioned a short while ago—that in the end he handed the man a container of water and said, “Go and pour it over yourself.”

A person in major impurity may perform tayammum on account of a wound even if water is present. Al-Walīd ibn ʿUbayd Allah ibn Abī Riyāḥ reported that ʿAṭāʾ told him from Ibn ʿAbbās that a man became junub in winter and asked about it, so he was instructed to perform ghusl.