Sahih Bukhari Volume 3, Book 34, Hadith Number 284.

Narated By ‘Aisha : When Abu Bakr As-Siddiq was chosen Caliph, he said, “My people know that my profession was not incapable of providing substance to my family. And as I will be busy serving the Muslim nation, my family will eat from the National Treasury of Muslims, and I will practise the profession of serving the Muslims.”