It was narrated from Miqdad bin Aswad that:
He asked the Prophet about a man who approached his wife, but did not ejaculate. He said: "If anyone of you finds that, he should sprinkle water over his private part (meaning he must wash it) and perform ablution." (IT)
English reference (IT): Vol. 1, Book 1, Hadith 505 (IT)
Arabic reference (IT): Book 1, Hadith 544 (IT)