It was narrated from Ibn 'Abbas that:
He came to Ubayy bin Ka'b accompanied by 'Umar. Ubayy came out to them and said: "I noticed some prostatic fluid, so I washed my penis and performed ablution. 'Umar said: "Is that sufficient?" He said: "Yes." He ('Umar) asked: "Did you hear that from the messenger of Allah?" He said: "Yes." (ES)
English reference (ES): Vol. 1, Book 1, Hadith 507 (ES)
Arabic reference (ES): Book 1, Hadith 546 (ES)