Musannaf Ibn Abi Shayba 1:1070

Abu al-Ahwas narrated to us, from ‘Ata’ ibn al-Sa’ib, from Sa’id ibn Jubayr, from Ibn ‘Abbas, who said: If a man becomes in a state of major ritual impurity (janabah) and he has a wound or smallpox, and he fears for himself if he performs ghusl (full body wash), he said: He should perform tayammum (dry ablution) with the soil.