Musannaf Ibn Abi Shayba 13:2221

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Al-A’mash narrated to us, from Shaqiq, from Masruq, from ‘Aisha, who said: Abu Bakr said during his illness in which he died: "Look at what has increased in my wealth since I entered into the Caliphate, and send it to the Caliph after me, for I had been using it lawfully, and I had been taking from the fat [provisions] an amount similar to what I used to take from trade." ‘Aisha said: When he died, we looked, and there was a Nubian slave who used to carry his children, and a camel used for drawing water that he used to irrigate with. She said: So we sent them both to ‘Umar. She said: My grandfather informed me that ‘Umar wept and said: "May the mercy of Allah be upon Abu Bakr; he has exhausted those who come after him with severe exhaustion."