Is saying, "O Lord, make me fatter so I can wear abayas," considered a vow, knowing that the intention was to wish for weight gain and to wear abayas that please God, without intending a vow, and is it permissible for a woman to wear modest skirts and blouses with abayas?

If the clothing worn by a woman fulfills the conditions of the lawful hijab, then wearing an abaya is not an obligation upon her according to Islamic law, but it is preferable, and a vow to wear it becomes binding. However, if her clothing does not fulfill the lawful conditions, then wearing an abaya or whatever fulfills these conditions becomes obligatory by original Islamic law, and a vow to perform an already obligatory act is not binding according to the majority of scholars. A vow becomes binding with any statement that indicates a commitment as an act of devotion to Allah, such as "It is incumbent upon me for the sake of Allah to do such and such." As for ambiguous phrases, a vow does not become binding through them except with a firm intention. It is obligatory for a Muslim woman to ensure that her clothing meets the conditions of the lawful hijab, for this is Allah's command and legislation. Allah Almighty says: "O Prophet, tell your wives and your daughters and the women of the believers to bring down over themselves [part] of their outer garments. That is more suitable that they will be known and not be abused. And ever is Allah Forgiving and Merciful."