In sum, this ḥadīth is a magnificent text on the subject of scrupulous piety: “Leave what puts you in doubt for what leaves you in no doubt.” Whatever stirs misgivings in you—abandon it, and hold fast to that which leaves you free of anxiety, uncertainty, and inner disturbance.

7/594 – ʿĀʾishah (Allah be pleased with her) said: Abu Bakr al-Ṣiddīq (Allah be pleased with him) had a slave who used to bring him a daily allowance from his earnings, and Abu Bakr would eat from it. One day the slave brought something and Abu Bakr ate of it. The slave then asked, “Do you know what that was?” Abu Bakr replied, “What was it?” He said, “In the Days of Ignorance I once practiced soothsaying for a man—though I was no real soothsayer; I merely deceived him. He met me today and, for that, gave me what you have just eaten.” Abu Bakr thereupon put his hand into his mouth and vomited everything that was in his stomach. Reported by al-Bukhārī.

[Explanation]
The ḥāfiẓ al-Nawawī (d. 676 AH) relates in his Riyāḍ al-Ṣāliḥīn, in the chapter on scrupulousness and avoiding doubtful matters, from ʿĀʾishah that Abu Bakr had a slave. Abu Bakr engaged him in a mukhāraja arrangement—that is, he would let him work and stipulate a fixed sum, saying, “Bring me such-and-such an amount each day, and whatever exceeds that is yours.”

This mukhāraja is permissible with slaves: if someone owns slaves and tells them, “Go out, work, and bring me each day this amount of dirhams; whatever is above that is yours,” then this is lawful, for the slaves belong to the master, and whatever they earn belongs to him all the same.