Advice for the seekers of knowledge–Don’t sleep too much!
The student of knowledge should sleep less as long as it does not harm his body and mind. He should not sleep more than eight hours in a day and night and that is a third (of one’s) time within a twenty four hour period. However, if he is able to sleep less, then he should do so.
[Original source: تذكرة السامع والمتكلم page: 77. Quoted by Shaikh Raslaan in Fadlul Ilm. Page: 281]