Sometimes it happens to me that I have a discussion with someone and he presents part of his unpublished works to me that help improving parts of my research.
Sometimes I use them in a paper in the way that after informing the person, I cite the results in my papers often by attaching that person’s name to his theorems and bringing them as unpublished notes or personal communication at the references. But I’m not sure whether the way that I cite such results is really correct or not.