Is it permissible to keep books inscribed with "Waqf for the mosque" without specifying a particular mosque, and how should they be dealt with?

The condition stipulated by the Waqif (endower) in a waqf (endowment) must be observed. Therefore, it is impermissible to dispose of it through sale, gift, or inheritance, based on the Prophet's (peace be upon him) statement to Umar ibn al-Khattab (may Allah be pleased with him) regarding the waqf of Khaybar: "Donate its core property; it is not to be sold, nor gifted, nor inherited, but its fruits are to be spent." If the books were endowed for a specific mosque, they must be returned to it. Otherwise, they should be placed in the mosque most in need of them.