OCS letter names

Hello everyone,

in the course of my research I arrived at a question that I don't know where to find the answer of. The question is: Where, in which ancient text, do we find the letters of the Slavonic alphabet listed with their coresponding names (азъ, боукьi, веди etc.) - which is the first historical attestation of these names? Does anyone have the answer?

My attempt to find out have brought nothing by now. And the question happens to be important.

Thank you in advance for any help.

Sincerely,

Evelina