Abu Zara' bin 'Amr /Harm أبو زرعة بن عمرو/هرم · Chapters On Al-Fitan

"It was said to 'Umar bin Al-Khattab: 'Perhaps you should endorse your successor.' He said: 'If I appoint a successor, then indeed Abu Bakr appointed a successor. And if I do not appoint a successor, the Messenger of Allah(s.a.w) did not appoint a successor."'