On his Rationalist Judaism blog, R' Natan Slifkin posed this question:
I am very interested to know if there are any early mentions of the phrase "l'iluy nishmas" or the concept thereof. (I am not referring to the concept of atoning for the departed via charity, but to the concept of elevating the soul, particularly via Torah learning.) My hunch is that it does not appear in the period of the Rishonim at all. Please let me know if I am wrong!
Do you know of any references to this concept from the period of the Rishonim or before?