Allah's Messenger ﷺ said: When any of you marries or buys a servant (slave woman), he should make this supplication:

اَللّٰهُمَّ اِنِّيْٓ اَسْاَلُكَ خَيْرَهَا وَخَيْرَ مَا جَبَلْتَهَا عَلَيْهِ وَاَعُوْذُ بِكَ مِنْ شَرِّهَا وَمِنْ شَرِّ مَا جَبَلْتَهَا عَلَيْهِ

O Allah! I ask You for her good and the good of the nature You created her with, and I seek refuge in You from her evil and the evil of the nature You created her with. And when someone buys a camel, he should take hold of the top of its hump and say this same supplication.

Sahih, Sunan Abi Dawud, no. (2160), the wording is his, Sunan Ibn Majah, no. (2252), Khalq Af'al al-Ibad of al-Bukhari, ed. al-Fuhayd, no. (208), and al-Albani graded it Sahih in “Adab az-Zifaf” (page 175).