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.

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[Original source: تذكرة السامع والمتكلم page: 77. Quoted by Shaikh Raslaan in Fadlul Ilm. Page: 281]