It is Sunnah to congratulate someone on their recent marriage by giving a dua to the newlywed. Several authenticated hadith sources support the sunnah of this dua. It was a habit of the Messenger of Allah to congratulate newly married people by praying for blessings upon them. This is reported in several authenticated collections of hadiths. Reported in Sunan Abi Dawud, Abu Hurayrah (رَضِيَ ٱللَّٰهُ عَنْهُ) narrated that when the Prophet Muhammad (ﷺ) congratulated a man on his marriage, he said: May Allah bless for you, and may He bless on you, and combine both of you in good (works). (Grade: Sahih (Al-Albani) Sunan Abi Dawud 2130). Similar accounts of this narration are reported in Jami` at-Tirmidhi (1091), Sunan Ibn Majah (1905), Mishkat al-Masabih (2445), and Bulugh al-Maram (Book 8, Hadith 6).
In Mishkat al-Masabih (2445), the following is explained: Abu Huraira said that when the Prophet congratulated a man on his marriage he said, “God bless you, bless you both, and prosper your union.” The verb used in prehistoric times to congratulate newly weds was raffa'a, which meant, "May the marriage produce close union and sons." The Prophet substituted raffa’a with the word used in this tradition. Thus, the verb simply develops the meaning of congratulating without involving any particular formula. (Ahmad, Tirmidhi, Abu Dawud, and Ibn Majah transmitted it.)
Home & Family Duas
The dua is a form of congratulations given to the newlyweds in Islam. The etiquette is to say the dua to the one married while congratulating him or her on their union. There is no particular way or method in which this dua should be said. You can say it as you like.
In Islam, when someone prays for the blessings and well-being of another Muslim, the angels of Allah pray the same upon the one praying. Another benefit of praying for blessings in a new marriage, including Allah’s acceptance, is that the new couple is protected from the temptations and interference of Shaytaan.