Reference: al-Hilyah – Volume 5, Page 121
Abu Moosaa al-Khowlaanee said:
Scholars are [of] three [types]:
1) A man who lived [his life] with his knowledge, and the people [around him] lived with him [and benefited from his knowledge]; and
2) A man who lived [his life] with his knowledge, and the people [around him] did not live with him [and so did not benefit from his knowledge]; and
3) A man whom people lived [and benefitted] with his knowledge, but he himself [did not, and as a result he] perished.