I am a senior Android dev, and I have an old colleague (iOS senior dev). We work on the same project, but in every estimation session he pushes a lot on the lower side: he estimates 4h a task that normally takes 6h or 8h, and the reason is that he has no social life. Right after work he starts working again from home (I can see all his commits), he also works almost entire weekends. I would say he works as average 12/13 h per day.
I don t want to work extra time (unpayed).
About him, it is his life, so I don t care...but at the same time this makes me pressure. I care a lot about quality of code, and I don t want to sacrifice it just for catching up. Most of the people in the team know that he works a lot extra time.

How would you handle this?

This is very sidetracking