Bulugh al-Maram #162

Narrated Ibn `Abbas (RAA): concerning the verse, “And if you are ill or on a journey...” (an-Nisa': 43). He said, "If a man sustains a wound, which he suffered during Jihad (in the cause of Allah) or ulcers, then he became junub (sexually impure) and is afraid that if he bathes he would die; he may perform ablution with clean earth (Tayammum). .