What is the limit for uttering a vow, and is mumbling, whispering, or moving the lips sufficient for it? And what is the meaning of articulating letters from their proper points of articulation?

We advise the questioner to fear Allah and to beware of extremism (excessiveness) and obsessive whispers (waswas). The form in which a vow (nadhr) becomes binding is what indicates the commitment, such as saying: "Upon me for Allah is such-and-such," or "I have vowed to Allah such-and-such." Utterance is essential; merely moving the lips without pronouncing the letters from their proper articulation points is not sufficient. Some scholars are of the opinion that one must also hear oneself.