Six years ago, my father gave me a sum of money equivalent to fifty-thousand Saudi Riyals and, after two years, I told him in a phone call that I wanted to pay Zakaah on this money. My father said that this money was a trust and that I did not have the right to pay Zakaah on it. Three years later, my father said that the money he deposited with me is now my own wealth.
My question is: Should I pay Zakaah on this money for the years when my father refused that I should pay it, or am I required to pay the Zakaah on it only after it became my own wealth?
May Allaah Grant you success to do what He Likes and Is Pleased with.
As-salaamu ‘alaykum.

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.

Scholars have stipulated conditions for Zakah to be obligatory on money. Among such conditions is that the money should belong to a specific owner because no Zakah is due on money that lacks an owner. Also, it is a condition that the money is fully owned by its owner.

Hence, you have to pay the Zakah on the money that was deposited with you by your father from the time he told you that he had gifted it to you. You should wait until one full lunar year passes after the date when you were notified that the money became yours and then pay an amount that equals a quarter of a tenth of its amount.

The author of Sharh Al-Muntaha said: "Zakah is not due on wealth whose sustainability is doubted because, in such a case, the cause of paying Zakah (i.e. the ownership of the wealth for a full lunar year) is not certain. Zakah is not due on wealth that is stolen or buried and forgotten. Nor is it due on inherited wealth whose heir is unaware of it because he had no knowledge about the death of his benefactor. It is also not due on unknown inherited wealth as is the case of an heir who knows that his benefactor died but does not know the place of the inherited wealth. The same applies to gifted wealth that was not received".

Since the money had been with you while you were not aware that it was gifted to you, then it takes the ruling of wealth that was not yet received. Hence, no Zakah is due on you until the time you came to know about the gift. Likewise, your father is not required to pay Zakah for this money after having gifted it to you.

As for the period during which the money was with you as a trust before being gifted to you, the majority of scholars view that Zakah is due on deposited money on behalf of its owner because he fully owns it even if he gifts it later to the one with whom he has kept it as a trust. This is because deposited money is fully owned by its owner. Thus, Zakah, which is the right of the poor, is due on it. The owner is not permitted to grant such a right to anyone other than those who deserve it from among the poor and needy.

Based on this, the Zakah of this sum of money is due on your father from the time he deposited it with you until he gifted it to you. If your father failed to pay its Zakah, pay it on his behalf for that period out of dutifulness to your father and to free his liability but not as an obligation. You should notify your father that you will do so in order for him to make the intention of paying Zakah because Zakah is an act of worship that is not valid without an intention. This is based on the statement of the Prophet, sallallaahu ‘alayhi wa sallam: "Deeds are based on intentions." [Al-Bukhari and others]

Allaah Knows Best.