It is narrated from Zubayd bin al-Salt that he said: I went out with Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) to al-Jurf. He looked and saw that he had had a wet dream, and he had prayed without taking a ritual bath. He said: By Allah! I did not know about the wet dream, and I prayed while I had not taken a ritual bath. Then he took a ritual bath and washed the place he saw on his clothes, sprinkled water on (the place) he did not see, gave the adhan and the iqamah, and prayed at that same place after the sun had risen high.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 801
It is narrated from Sulayman bin Yasar that Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) led the people in the morning prayer, then went to his land at al-Jurf and found traces of a wet dream on his clothes. Then he said: When we began eating rich (fatty) food, the veins softened.
Then he took a ritual bath, washed the traces of the wet dream from his clothes, and repeated the prayer.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 802