What is the ruling on donating money to Allah from an inheritance that is mortgaged with debts equal to its value?

The wording uttered by your husband is considered a vow by some jurists, even if it lacks a word indicating commitment. This is the fatwa we adhere to if he intended it as a vow.

If your husband said that with the intention of making a vow, then he must fulfill it once he receives his share of the inherited apartment, based on the Prophet's (peace be upon him) saying: "Whoever vows to obey Allah, let him obey Him."

If he did not specify a certain amount, then he may spend whatever amount he wishes, even if small, and its distribution should be to the poor as an absolute charity.