Does a divorce occur if a husband says to his wife: "I swear by divorce, tomorrow morning you will receive a divorce; I swear by God, you will receive a divorce tomorrow," but then nothing happens the next day and they reconcile?

The fatwa is that swearing by divorce results in divorce upon breaking the oath. This is the view of the majority of scholars. Shaykh al-Islam Ibn Taymiyyah, however, holds that its ruling is like swearing by Allah, and it necessitates an expiation for an oath (kaffarat yamin) upon breaking it, without divorce taking place. Accordingly, since you broke your oath not to divorce your wife, a divorce has occurred, and you are obligated to offer an expiation for an oath for swearing by Allah. If you have not divorced her more than once before, you can take her back (raj'ah) before her waiting period (iddah) expires. It is advised to avoid swearing by divorce.