What is the ruling on a husband saying, "I divorce my wife if I do such-and-such" during an argument with his sister, if he does not do what he swore to do? Is it considered a divorce, or is he bound by an expiation for breaking an oath?

If a husband swears an oath of divorce to do something, and then breaks his oath, the divorce occurs according to the majority of scholars, and this is the most preponderant opinion. The breach of oath occurs if he specified a time for the action and did not perform it until the time elapsed, or if he did not specify a time and it became impossible to perform the action. However, if the husband did not intend divorce, he is obligated to offer an expiation for breaking an oath, according to Sheikh al-Islam Ibn Taymiyyah. If the divorce occurs, he can take his wife back before her 'iddah (waiting period) expires, provided that this divorce does not complete the third divorce.