The advice of Imam Malik (Rahimahullah) to Imam Shafi'i (Rahimahullah)

"Allah Ta'ala has casted a Nur (light) in your heart, so do not extinguish it with sins."

Note:

'Ilm is a Nur from Allah Ta'ala which Allah Ta'ala does not grant to a person who is immersed in sins. A little knowledge is a lot when a person abstains from sins. But a lot of knowledge without abstaining from sins is like a donkey that carries a lot of books on its back without being able to benefit from them. The essential thing is the obedience of Allah Ta'ala and not the acquisition of more knowledge. That is why one must choose a person who is really practicing and is Deendaar to learn Deen from. It does not suffice that he has  a lot of knowledge if he is not serious in Deen.

[English version of "Conseil de Imam Malik (R) à Imam Shafi (R)" – Al Jamiat – Vol.5 No.14]