source of mind.mind-sources.
或
to think of the source
供参考:
饮水思源
grateful for favors received or not to forget one's origins
[谚]不要污染你曾经饮过的泉水；饮水思源
Never cast dirt into the fountain of which you have sometime drunk.
两思（致富思源,富而思进）
to think of the source of getting rich and of making progress after becoming affluence
