What is the ruling on a gift that consists of one person giving their future salary to another, knowing that the donee was not present at the time of the gift, and is the presence and knowledge of the donee a condition for the gift to be effective?

A person's statement that he will give his salary to another is not a gift, but rather a promise of a gift, and thus is not binding. A gift, according to the majority of scholars, is not binding until it is taken possession of. So, if someone gifts something to an absent person, and the recipient is unaware of it, then neither acceptance nor possession has occurred, and therefore his gift is not effective.