Shulchan Aruch HaRav, Laws of Torah Study 4:14

Needless to say, a person who studies in order to become great and to have a name like that of the great scholars of the land, or to earn a livelihood in teaching, judging or instructing, keep in mind that the Sages say not to make [words of Torah] into a crown through which to glorify yourself nor into a hatchet to cut with, for all who profit from Torah take their life out of the world. Rather speak [words of Torah] for their own sake and for the sake of them serving God. But even so, one who does not fear God [enough] to speak words of Torah for their own sake but instead learns in order to become great or to earn a living, it is better that that person learn Torah not for its own sake rather than not learning at all or separating from learning, for through the process of doing it for ulterior motives, that person will come to do it for the right reasons, as discussed above. [AJWS translation]