It was narrated from Abu Hurairah:
that the Prophet used to say, when offering congratulations of the occasion of marriage: "Barak Allahu lakum, wa barak 'alaikum, wa jama'a bainakuma fi khair (May Allah bless you and bestow blessings upon you, and bring you together in harmony)."
English reference: Vol. 3, Book 9, Hadith 1905
Arabic reference: Book 9, Hadith 1980