Citing a funding application in a student thesis
The rule with citation of “unusual” references is always something like that:


Make sure you really want to cite it. (In your case, it sounds okay, but most cases of students trying to cite “unusual” stuff end up with me telling them not to cite it)
Include just enough information that the cited item is uniquely identifiable.
If the item is not publicly available, include additional information that hints at its content (such as the title).


For example:


  John Aristotle (341 BC). Exploring the impact of introducing a fifth element in Empedocles’s classification of principles [Grant X1FH25 proposal to the Macedonian Science Fundation, Agency for Philosophical Research].