Spellbook

• WWizards of the Coast2009-10-01
  Official Ruling
  If multiple effects modify your hand size, apply them in timestamp order. For example, if you put Null Profusion (an enchantment that says your maximum hand size is two) onto the battlefield and then put Spellbook onto the battlefield, you'll have no maximum hand size. However, if those permanents entered in the opposite order, your maximum hand size would be two.

Rulings via Scryfall