This is not correct.

It is good to have ablution before you sleep but this doesn’t mean that the angels will wake you up for fajr .My advice to you is that you should sleep early in the night and you should drink a lot of water before going to bed.

Sometimes I don’t wudu before sleeping at night and in many cases I missed Fajr,is this because I didn’t wudu?If I take wudu,will the angels wake me up for fajr?