Indirect words plus intention make a vow binding
4-8-2015 | IslamWeb
Question:
My uncle's wife did not visit her mother-in-law due to some problems. Her mother-in-law once said: "If my son's wife comes to my house, I will invite the household to such-and-such food." Is this considered a vow? Is it permissible for us to eat from that food on the basis that we are invited?
Answer:
All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.
A vow is a pledge made by a person who is competent for religious assignment to willingly do an act of obedience to Allaah Almighty although he is not obliged by the Sharee'ah to do it. The vow becomes binding when it is said with any wording signifying pledge and commitment such as, 'I will fast such–and-such day for the sake of Allaah', 'If Allaah heals me, I will give such and such in charity', and so on.
The wording in question does not signify commitment. Consequently, it is not considered a vow. Fulfillment is not due unless the woman in question intended it to be a vow. In order to be binding, intention is crucial for the vow with indirect words. If we assume that she did not intend a vow, then it is a promise and it is recommended to fulfill it. However, according to the majority of scholars, she is not guilty for not fulfilling it. Nevertheless, it is strongly recommended to fulfill one's promise and strictly disliked to break it. Allaah Almighty says (what means): {O you who have believed, why do you say what you do not do? Great is hatred in the sight of Allaah that you say what you do not do.} [Quran 61: 2-3] Praising His Prophet Isma‘eel (Ishmael) 
Allaah Almighty says (what means): {He was true to his promise, and he was a messenger and a prophet.} [Quran 19: 54]
The Prophet, sallallaahu ‘alayhi wa sallam, considered breaking promises one of the traits of the hypocrites, saying: "The signs of the hypocrite are three: whenever he speaks, he tells lies; whenever he makes a promise, he breaks it; and whenever he is entrusted with something, he betrays the trust." [Al-Bukhari and Muslim]
You are permitted to eat from this food for, even if we assume that it is a vow, your uncle's wife has dedicated it to the household, which includes you.
Allaah Knows best.