Is money paid to a deceased friend in a commercial agreement, which his father denies, considered a debt that warrants claiming, and is Zakat obligatory on it?

If the money was invested and did not incur a loss, the business must be liquidated, and the capital and profit share returned. If the business incurred a loss due to the negligence of the one in charge, then he must return the capital, and it is considered a debt upon him.

A debt owed by the deceased must be paid from his estate before the inheritance is distributed. The heirs are not obliged to pay the debt merely upon a claim, but rather upon proof, such as testimony, an oath, or the deceased's handwriting. If the deceased left nothing, the heirs are not obliged to pay on his behalf, though it is commendable for them to do so to clear his conscience.

Zakat (definition) is not obligatory on a debt that is denied, owed by an insolvent person, or by one who procrastinates, except upon its collection. When collected, zakat is paid for one year only.