Mishkat al-Masabih 2446

'Amr b. Shu'aib, on his father’s authority, said his grandfather told how the Prophet (ﷺ) said that when anyone of them married a woman, or bought a servant he should say, “O God, I ask You for the good in her and in the disposition You have given her, and I seek refuge in You from the evil in her and in the disposition You have given her.” When he buys a camel he should take hold of the top of its hump and say the same kind of thing. In a version regarding a woman and a servant it says he should take hold of her forelock and make supplication for a blessing. Abu Dawud and Ibn Majah transmitted it.