**EDIT: This is the second version of the question, question clarified**

I work in a company in a team, let's say A's team. There is also in the close group of workers, B, with whom I am working right now. And there is C, the manager of al A's team (including me), and B.

Note that C is the only one here with "hierarchy power" on us (assessment, payrises...). B is a tech worker, I am a tech worker, A is managing with no hierarhy power.

I worked with B for a long time. Everything was not fine, but that's another story. Then I continued alone and B went on other tasks.
BUT: B is an older worker than me, with more knowledge on the task: currently, B always asks me about how I am performing on the task. I think B's motives for such questions are 1/ technical interest in the task ("mine"), and 2/ lack of interest in current B's task (which I am not related to). The result however is that B looks like spending time on my task and not on B's task, while I don't (always) need B to come help me on my task.

A is aware of the situation, A has seen already B coming to me and saying:
B: "Hey, what's up on the task?"
"[Me answering]"
B: "Ok, next steps should be that and that, let's look together"
And I can't manage to put B out.

A told me about what he saw: "I know B is coming to work on your task, and not on his task. But I am not chief of B so I won't tell him to stop." I understand. I tried to tell B something along the lines: "Thanks for helping but don't feel forced to do so if you have other things to do".

So right now, the situation is:

* Me and B are working on my task
* B is not working on his task
* A is aware and have interests on both tasks, authority on my task

Problem is C, with hierarchic power, has reports from me by mail, and regular spoken reports from A and B. I don't think, since B is in the same meeting as A, that A raised the problem to C during their spoken reports. In my mail, I can't say neither that B intervened. I just say how tasks are going on.

So question is: I think I should convey the info about B's behaviour to C. I can ask C for a short meeting, but how could I convey, professionnally, the situation I described above?