Yusuf bin Muhammad said: It reached me that Sayyiduna Abu Bakr al-Siddiq (may Allah be pleased with him), during his illness, dictated a will to Sayyiduna Uthman (may Allah be pleased with him): 'Bismillahir-Rahmanir-Rahim' (In the name of Allah, the Most Gracious, the Ever Merciful). This is the will of Abu Bakr bin Abi Quhafah at the time of his departure from this world, when even the liar speaks the truth, even the treacherous one fulfils the trust and even the disbeliever thinks of believing. I nominate Sayyiduna Umar (may Allah be pleased with him) as successor after me. If he acts justly, then that is my opinion of him and my hope in him; and if he does wrong and transgresses, then I do not know the unseen, and every person will have what he has earned: "And those who have wronged will come to know to what return they will be returned" [Surah al-Shu'ara: 227].
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قتال أهل البغي / 16576