For the groom, and when buying an animal
For the groom, and when buying an animal: 1 supplication in Arabic with English translation and sources, from the Fortress of the Muslim (Hisn al-Muslim).
دعاء المتزوج و شراء الدابة
إِذَا تَزَوَّجَ أَحَدُكُمُ امْرَأَةً، أَوْ إِذَا اشْتَرَى خَادِماً فَلْيَقُلْ: اللَّهُمَّ إِنِّي أَسْأَلُكَ خَيْرَهَا، وَخَيْرَ مَا جَبَلْتَهَا عَلَيْهِ، وَأَعُوذُ بِكَ مِنْ شَرِّهَا، وَشَرِّ مَا جَبَلْتَهَا عَلَيْهِ، وَإِذَا اشْتَرَى بَعِيراً فَلْيَأْخُذْ بِذِرْوَةِ سَنَامِهِ وَلْيَقُلْ مِثْلَ ذَلِكَ.
When one of you marries a woman or buys a servant, let him say: “O Allah, I ask You for her good and the good of the disposition You have given her, and I seek refuge in You from her evil and the evil of the disposition You have given her.” If he buys a camel, let him take hold of the top of its hump and say the same.
Fortress of the Muslim (Hisn al-Muslim), Sa‘id ibn ‘Ali al-Qahtani. MushafPlus translation made from the Arabic, not reviewed by a specialist.