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
اللَّهُمَّ 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.
Sahihرَبَّنَا 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 أَسْأَلُكَ حُبَّكَ وَحُبَّ مَنْ يُحِبُّكَ وَحُبَّ كُلِّ عَمَلٍ يُقَرِّبُنِي إِلَى حُبِّكَ
O Allah, I ask You for Your love, the love of those who love You, and the love of every deed that brings me closer to Your love.
Hasan