Du'a for newly married

بَارَكَ اللَّهُ لَكَ وَبَارَكَ عَلَيْكَ وَجَمَعَ بَيْنَكُمَا فِي خَيْرٍ

Barakallahu laka wa baraka 'alayka wa jama'a baynakuma fi khayrin

May Allah bless you, and send blessings upon you, and bring you both together in goodness.

Sunan Abī Dāwūd 2130, Jāmiʿ al-Tirmidhī 1091