Is expiation (kaffarah) obligatory for one who swore to abandon cigarettes and shisha, then returned to them, or is sincere repentance sufficient?

Shisha is forbidden (haram), and quitting it is obligatory. If someone has sworn an oath to quit it, it is not permissible for him to break his oath, because smoking is inherently forbidden (haram). Engaging in it after taking an oath leads to the sin of committing a forbidden act and breaking an oath, and thus requires an expiation for the oath (kaffarat al-yamin). The expiation for an oath is: feeding ten poor persons, or clothing them, or freeing a slave. If one cannot find these, then fasting for three days, as Allah the Almighty says: "Allah will not impose blame upon you for what is unintentional in your oaths, but He will impose blame upon you for what you intended in your oaths. So its expiation is the feeding of ten poor persons from the average of that which you feed your [own] families or clothing them or the freeing of a slave. But whoever cannot find [or afford it] - then a fast of three days. That is the expiation for oaths when you have sworn. And guard your oaths. Thus does Allah make clear to you His verses that you may be grateful." (Surat Al-Ma'idah, 5:89). He must also offer sincere repentance along with quitting smoking. Repentance does not nullify the expiation, because expiation is a mandatory right.