Does a vow become binding if it is not accompanied by an oath?

Question:
He says: … It is forbidden for me, or I have vowed, or it is upon me for Allah that I will not eat such-and-such, or I will not drink such-and-such. The stronger of the scholars' opinions is that it does not become binding unless it is accompanied by an oath, in which case an expiation for an oath is required of him?

Answer:
No, the correct view is that it becomes binding, but an expiation for an oath is required. The correct view is that it becomes binding; it is a valid vow, and an expiation for an oath is required of him, unless it involves a sin. In that case, he must not fulfill the vow in the sin, and an expiation is required of him according to two opinions. The stronger opinion is that an expiation is required even in a vow of sin, as long as he is a Muslim, as long as it is not a vow of shirk (associating partners with Allah). For this reason, in Sahih al-Bukhari: "The expiation for a vow is the expiation for an oath."
It should be known that most scholars, especially the early ones, were unaware of certain matters of the Sunnah. They would rule based purely on their independent legal reasoning, according to what reached them of the Sunnah. Then the Sunnah would reach those who came after them, who collected it and took care of it, and rulings would become apparent to them that had not been apparent to those before them because some of the Sunnah was hidden from them. Not everyone collects the hadiths and memorizes them all.