specified it. Whatever the Sacred Law mentions without defining it is referred back to customary practice, as the poet said:

Whatever comes without being defined
by the Sacred Law—such as secure custody—define by customary practice. (1)

This is why the author says, “unless they have separated physically according to customary practice.”

But how is physical separation determined according to customary practice?

The answer is that we consider the circumstances. If they are walking from the congregational mosque to the religious institute, and he sells it to him at the mosque, and they then walk together toward the institute—a walk that takes at least one-third of an hour—then these two men retain the option until they separate at the institute. So long as they continue walking together, accompanying one another, they retain the option.

If they are in a room and conclude a sale, then one of them leaves the room for the restroom to relieve himself, they have separated, because the first session has ended.

If they are on an airplane bound for a distant destination, a journey of thirteen hours, and they conclude a sale when it takes off, while it will not land until thirteen hours later, then the period of the option is thirteen hours, so long as they have not separated. The solution to this problem is for them to conclude the sale on the condition that there be no option. This is why the Prophet, peace and blessings be upon him, said in the hadith: “If one of them gives the other the choice, and they conclude the sale on that basis, then the sale becomes binding.” (2)

That is, they waive the option and conclude the sale on the condition that there be no option, such that as soon as the offer and acceptance are made, the sale becomes binding and there is no option.