How to use data from a colleague who retired in my thesis without commiting fraud or plagiarism
As PatW says in a comment: the general correct action in this case is coauthorship. This gets a little bit trickier with a thesis, which does not typically allow coauthors per se. For the thesis, the thing you should do is give explicit credit where the data is introduced. If it corresponds with the practices of your field, you can also put in a citation to your colleague as an unpublished document or personal communication.

When you republish this material as a journal manuscript or other conventional form that allows multiple authors, however, your colleague should be amongst the set of coauthors.