Are the following statements considered an oath (yameen) and do they necessitate expiation: "O Allah, forbid Paradise for me if I do such-and-such," "O Allah, I will do such-and-such, and hold me to my word," and "O Allah, if I do such-and-such, then I am a disbeliever"?

The statement, "O Allah, forbid Paradise for me if I do such-and-such," or "O Allah, if I do such-and-such, then I am a disbeliever," is not considered an oath, and no expiation is required for it. However, a Muslim should avoid such expressions. As for the statement, "O Allah, I will do such-and-such, and take me by my word," this is a promise and is not considered an oath, nor does it require expiation, unless the promised action is obligatory and the promise was emphasized with Allah.