is it true that new born baby generally do not sleep beyond 3 hours?

It depends on the baby! Mine occasionally slept 5 hours during the first 2 weeks until we started to wake her up for feeds every 3 hourly. For the first month at least, they need to be fed at least 3 hourly. This was recommended by my lactation consultant. My baby slept anywhere from 4-8 hours at 5-7 weeks. But currently my bb is 15 weeks old and she has sleep regression, so the sleeping pattern is quite erratic for now.