Halocho #923 - Borrowers can't be lenders

If you borrow, rent or hire something, you are not allowed to let other people use it, without explicit permission from the original owner.

If one knows for a fact that the owner allows this particular person use this item (or similar items) then one can lend or rent the item to that person.

Even though it's a Mitzva to let other people use your Sefarim (Torah related books), if you borrow a Sefer you may not let others use it.

If one borrows a Sefer and is given permission for others to also use it, only one person at a time may use it.

Source: Kitzur Shulchan Aruch 185:1

- Danny
Sunday, 16 Marchesvan 5772