Is PhD stipdent tax free if I have external funding?



I took my own project to a university and found funding through a range of small grants for my stipend. These grant funds will be sent to the charity I also work for and paid to me monthly from that charity. I was wondered if this stipend will still be tax free, and if I need to do anything to prove it is a stipend and not income from paid work?

Thanks so much for any advice you can give