Sayyiduna Amr bin al-As (may Allah be pleased with him) was (in command) over a military detachment. They were struck by severe cold, the like of which had not been seen before. He came out for the Fajr prayer and said: By Allah, I had a wet dream last night, but by Allah, I have never seen cold like this; has anything like it ever passed over your faces? They said: No. Then he washed the folds of his body and performed ablution like the ablution for prayer, and then led them in prayer. When they came to the Messenger of Allah (peace and blessings be upon him), the Messenger of Allah (peace and blessings be upon him) asked: "How did you find Amr and his companions?" They praised him well and said: O Messenger of Allah, he led us in prayer while he was junub. The Messenger of Allah (peace and blessings be upon him) sent for Amr and asked him, and he told him the whole incident and also about the cold he had suffered. He said: O Messenger of Allah, Allah Almighty says: "And do not kill yourselves" [Surah al-Nisa': 29]; if I had taken a ritual bath, I would have died. The Messenger of Allah (peace and blessings be upon him) laughed, looking towards Amr.
(b) The Shaykh said: It is possible that he did what is reported in both narrations together: he washed what he was able to wash and performed tayammum for the rest.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 1071