´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).”
Related hadith on this topic
Explanation & Benefits
Shaykh Umar Farooq Saeedi
Benefits and Issues:
On such occasions of happiness, one should offer pure and Sunnah supplications as congratulations, which encompass all apparent and hidden meanings of affection, love, and increase.
Source: Sunan Abu Dawood – Commentary by Shaykh Umar Farooq Saeedi, Page: 2130