Abu Musa reported Allah’s Apostle (peace be upon him) as saying: The similitude of that guidance and knowledge with which Allah, the Exalted and Glorious, has sent me is that of rain falling upon the earth. There is a good piece of land which receives the rainfall (eagerly) and as a result of it there is grown in it herbage and grass abundantly. Then there is a land hard and barren which retains water and the people derive benefit from it and they drink it and make the animals drink. Then there is another land which is barren. Neither water is retained in it, nor is the grass grown in it. And that is the similitude of the first one who develops the understanding of the religion of Allah and it becomes a source of benefit to him with which Allah sent me. (The second one is that) who acquires the knowledge of religion and imparts it to others. (Then the other type is) one who does not pay attention to (the revealed knowledge) and thus does not accept guidance of Allah with which I have been sent.
Sahih Muslim, Book 43, Hadith 16