Is Zakat obligatory on money for which one has not prayed, and on usurious gains that have been spent on necessities?

Money acquired through unlawful means, such as usury, has its prohibition linked to the earner's responsibility, not to the money itself. Consequently, it is not forbidden to deal with someone who earned it through lawful means.

This is supported by the fact that the Prophet, peace and blessings be upon him, dealt with the Jews who consumed illicit gains and usury. His dealings with them indicate that what is forbidden in its earning is not forbidden to someone other than the earner.

Therefore, money taken from the father through lawful means—such as a gift—does not necessitate disposal, and Zakat is obligatory on it if it reaches the nisab (minimum threshold) and a full year has passed.

If Zakat has not been paid on these monies received from the father, repentance is obligatory, and the Zakat for previous years must be paid, because Zakat is not waived by statute of limitations.