When the Prophet ﷺ congratulated someone on their marriage, he would say, "May Allah bless you, may He shower His blessings upon you, and may He unite you both in goodness."
حدثنا سويد بن سعيد حدثنا عبد العزيز بن محمد الدراوردي عن سهيل بن أبي صالح عن أبيه
أن النبي ﷺ كان إذا رفأ قال بارك الله لكم وبارك عليكم وجمع بينكما في خير
[Sahih] Abu Dawud narrated it in the Book of Marriage, chapter on what is said to a person who has married, no. 2130, through Abdul-Aziz Darawardi. Tirmidhi graded it sahih, no. 1091, as did Ibn Hibban, Hakim, and Dhahabi.