How can it be imagined that a master would permit his slave to make a vow?

Question : But how can it be imagined that a master would prevent his slave from making a vow? It is possible if the slave says to his master, for example, "I want to make a vow regarding my success in such-and-such," and he says, "I have a vow upon me to Allah: if I succeed, I will perform Hajj."

Answer : And his master has permitted him to do so. This is possible, even though a vow, as you know, is disliked, and some scholars have forbidden it. This is because the Prophet (peace and blessings be upon him) prohibited it, saying that it does not bring good, that it does not avert anything, and that it does not advance or delay anything. All of this is established in the authentic collections. And the Messenger (peace and blessings be upon him) spoke the truth when he said that if Allah the Exalted wills a decree, He decrees it, whether you make a vow or not. However, Allah may extract from you through this vow because you are stingy, or He may extract from you an act of worship because you do not perform acts of worship. That is why so many people regret it when they make a vow, and then they come to the doors of the scholars asking, "What is the ruling on this?"