Reference for Avodah Zarah 44:8

אלא הא דתני רב יוסף ארמלתא לא תרבי כלבא ולא תשרי בר בי רב באושפיזא בשלמא בר בי רב צניע לה אלא כלבא כיון דמיגרה בה מרתתא

Then what about that which R. Joseph taught: “A widow should not rear dogs, nor accommodate a student as a guest”? Now this makes sense in the case of a student, as she might rely on his modesty, but in the case of a dog why not say that she would be afraid of being followed about by it?

Jastrow