Bukhari

Hadith Commentary:
That is, now that I will be occupied with the duties of the caliphate, I will not have the opportunity to pursue my personal profession or to frequent the markets. Therefore, I will take the expenses for myself and my family from the public treasury (bayt al-mal). And I will also manage these expenses in such a way that, by engaging in trade and commerce with the funds of the bayt al-mal, I will increase it and bring benefit to the Muslims.

Hadith Commentary:
(1)
Abu Bakr as-Siddiq radi Allahu anhu used to engage in the cloth trade before becoming the Caliph, and he would earn for his household himself. Ibn Sa'd has narrated a mursal report that when Sayyiduna Abu Bakr radi Allahu anhu was elected as Caliph, he, according to his habit, lifted a bundle of cloth on his head and set out for the market. Umar and Abu Ubaydah ibn al-Jarrah radi Allahu anhuma asked him: "Where are you going?" He replied: "I intend to go to the market for trade." Consequently, after mutual consultation, they fixed a stipend for him. (Fath al-Bari: 4/385) From this, it is understood that a government ruler may take a wage from the Bayt al-Mal (public treasury).

(2)
Abu Bakr as-Siddiq radi Allahu anhu did not invest government wealth in business, as is commonly thought. If he had enough time, he would have conducted his own business and not burdened the Bayt al-Mal; rather, he would supervise and look after the affairs of the Muslims, in return for which a sufficient stipend was fixed for him from the Bayt al-Mal. (Fath al-Bari: 4/386)