Is taking profits after promising not to a sin, and am I obligated to return them?

The majority of scholars are of the view that fulfilling a promise is recommended (mandub/mustahabb) and not obligatory (wajib). One who does not fulfill it incurs no sin, but commits something disliked (makruh), a disliking of tanzih (a lesser degree of disliking). Therefore, it is better to fulfill your promise to earn reward, but if you do not fulfill it, there is no sin upon you regarding the profits you have taken.