Dua #1073•Abu Dawud 2/248 and Ibn Majah 1/617. See also Al-Albani, Sahih Ibn Majah 1/324.

On the wedding night or when buying an animal

Hisnul Muslim
#1073

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.

Transliteration

Allāhumma innī as'aluka khayrahāwa khayra mā jabaltahā `alayh. wa a`ūdhu bika min sharrihāwa sharri mā jabaltahā `alayh.

Translation

When any of you marries a woman or purchases a maid-servant then let him say: O Allah, I ask You for the goodness of her, and the goodness upon which You have created her, and I seek refuge in You from the evil of her, and from the evil upon which You have created her. If you purchase a camel then take hold of the top of its hump and say the same.