I think this is "magic words" question. And in natural languages there are no magic words.
There is no single set phrase that you need to use. This would naturally occur as part of a conversation with input from both you and the student. Can you imagine a student going to see their supervisor who says. "Use these books as a reference" and then is silent?
Instead imagine what the conversation could be like.
T: Hello. ... Chat about how things have been last week...
T: Now I'd like you to elaborate your knowedge.
S: Okay — what do you mean by that?
T: Well I'd like you to read around the topic. You could refer to — Let's see now, Spivak is a good source for basic calculus but for a more in depth analysis you should read chapters 6-9 of Berkely.
S: Is that in the library.
T: Actually I think I have a copy here... yes, now. Here are some other books to use as references. Bostock and Chantler, Bolt and Reynolds — yes that is good for point-set topology. You can use that to answer your questions on the axiomatic approach to continuity.
Do you see?
There is nothing incorrect about "Use these books as references." but on its own it lacks context. A meeting between two people will always be a conversation. There is no one right way to say it.