Urwah bin al-Zubayr (may Allah have mercy on him) narrates from Sayyidah Aishah (may Allah be pleased with her) that when Sayyiduna Abu Bakr al-Siddiq (may Allah be pleased with him) became caliph, he said: My people know that I used to bear the expenses of my family from my trade, but now I am occupied with the affairs of the Muslims; so the family of Abu Bakr will now take their expenses from the public treasury (bayt al-mal), and I will work for the Muslims.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب آداب القاضي / 20288