Is one obligated to fulfill a vow (nadhr) if income is insufficient for household needs, and do household needs take precedence over charity (sadaqah) and vows?

The one who makes a vow must give in charity what he vowed, in the specific category he designated. If he is unable to fulfill his vow, the vowed item remains a debt upon him, which he must discharge when he is able. In this case, no expiation is required of him. However, if the inability is not expected to be temporary, then he must offer an expiation for breaking an oath: feeding ten needy persons, or clothing them, or freeing a slave. If he is unable to do so, then he must fast for three days. If he is able to give some of the vowed item but not all, he should give in charity what he can, and he must offer expiation for what he was unable to give. If he is unable to ascertain the exact amount that must be given, he must make an effort to estimate it and give what will lead to certainty or strong probability of clearing his liability.