When any of you marries a woman or purchases a maid-servant then let him say: O Allah, I ask You for...
Reference:Abu Dawud 2/248 and Ibn Majah 1/617. See also Al-Albani, Sahih Ibn Majah 1/324.Hisnul Muslim 191
(اللَّهُمَّ إِنِّي أَسْأَلُكَ خَيْرَهَا وَخَيْرَ مَا جَبَلْتَهَا عَلَيْهِ وَأَعُوذُ بِكَ مِنْ شَرِّهَا وَشَرِّ مَا جَبَلْتَهَا عَلَيْهِ)
Allāhumma innī as'aluka khayrahāwa khayra mā jabaltahā `alayh. wa a`ūdhu bika min sharrihāwa sharri mā jabaltahā `alayh.
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.