Is it permissible to retract a promise to give a monthly charity to a needy person due to unforeseen circumstances, or is the promise binding?

First: Fulfilling a promise is considered mustahabb (recommended) by the majority of jurists. Some scholars, like Umar ibn Abd al-Aziz and Ibn Taymiyyah, held the view that it is wajib (obligatory) absolutely, and this is the more preponderant opinion. If fulfilling the promise becomes difficult, one should then appease the promised person and explain what happened.

Second: It is forbidden to revoke a sadaqah (charity) after the poor person has taken possession of it. However, before possession, it is not forbidden. If a Muslim sets aside something for charity but the poor person has not yet taken possession of it, then he is permitted to revoke it, though it is recommended to proceed with it.