بَارَكَ اللَّهُ لَكَ وَبَارَكَ عَلَيْكَ وَجَمَعَ بَيْنَكُمَا فِي خَيْرٍ
Barakallahu laka wa baraka 'alayka wa jama'a baynakuma fi khayr
May Allah bless you and shower His blessings upon you, and bring you both together in goodness.
This is the Sunnah way to congratulate newlyweds. The Prophet ﷺ taught this instead of the pre-Islamic congratulation which focused on worldly wishes. This du'a focuses on barakah (divine blessing) and goodness in the union.
Related Du'as
رَبَّنَا هَبْ لَنَا مِنْ أَزْوَاجِنَا وَذُرِّيَّاتِنَا قُرَّةَ أَعْيُنٍ وَاجْعَلْنَا لِلْمُتَّقِينَ إِمَامًا
Our Lord, grant us from among our spouses and offspring comfort to our eyes, and make us a leader for the righteous.
Sahihاللَّهُمَّ إِنِّي أَسْتَخِيرُكَ بِعِلْمِكَ وَأَسْتَقْدِرُكَ بِقُدْرَتِكَ وَأَسْأَلُكَ مِنْ فَضْلِكَ الْعَظِيمِ فَإِنَّكَ تَقْدِرُ وَلَا أَقْدِرُ وَتَعْلَمُ وَلَا أَعْلَمُ وَأَنْتَ عَلَّامُ الْغُيُوبِ اللَّهُمَّ إِنْ كُنتَ تَعْلَمُ أَنَّ هَذَا الْأَمْرَ خَيْرٌ لِّي فِي دِينِي وَمَعَاشِي وَعَاقِبَةِ أَمْرِي فَاقْدُرْهُ لِي وَيَسِّرْهُ لِي ثُمَّ بَارِكْ لِي فِيهِ وَإِنْ كُنتَ تَعْلَمُ أَنَّ هَذَا الْأَمْرَ شَرٌّ لِّي فِي دِينِي وَمَعَاشِي وَعَاقِبَةِ أَمْرِي فَاصْرِفْهُ عَنِّي وَاصْرِفْنِي عَنْهُ وَاقْدُرْ لِيَ الْخَيْرَ حَيْثُ كَانَ ثُمَّ أَرْضِنِي بِهِ
O Allah, I seek Your guidance through Your knowledge, and I seek ability through Your power, and I ask of Your great bounty. You are capable and I am not. You know and I do not. And You are the Knower of the unseen. O Allah, if You know this matter is good for me in my religion, my livelihood, and the outcome of my affairs — decree it for me, make it easy for me, and bless me in it. And if You know this matter is bad for me in my religion, my livelihood, and the outcome of my affairs — turn it away from me and turn me away from it, and decree for me what is good wherever it may be, then make me content with it.
Sahihاللَّهُمَّ اجْعَلْ بَيْنَنَا مَوَدَّةً وَرَحْمَةً وَسَكِينَةً، وَأَلِّفْ بَيْنَ قُلُوبِنَا وَاجْعَلْنَا قُرَّةَ أَعْيُنٍ لِبَعْضِنَا
O Allah, place between us affection, mercy, and tranquility. Unite our hearts and make us the coolness of each other's eyes.
Sahihرَبَّنَا أَفْرِغْ عَلَيْنَا صَبْرًا وَتَوَفَّنَا مُسْلِمِينَ
Our Lord, pour upon us patience and let us die as Muslims.
Sahih