Sahih Bukhari Volume 9, Book 93, Hadith 7220

حَدَّثَنَا مُحَمَّدُ بْنُ يُوسُفَ، أَخْبَرَنَا سُفْيَانُ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ ـ رضى الله عنهما ـ قَالَ قِيلَ لِعُمَرَ أَلاَ تَسْتَخْلِفُ قَالَ إِنْ أَسْتَخْلِفْ فَقَدِ اسْتَخْلَفَ مَنْ هُوَ خَيْرٌ مِنِّي أَبُو بَكْرٍ، وَإِنْ أَتْرُكْ فَقَدْ تَرَكَ مَنْ هُوَ خَيْرٌ مِنِّي رَسُولُ اللَّهِ صلى الله عليه وسلم فَأَثْنَوْا عَلَيْهِ فَقَالَ رَاغِبٌ رَاهِبٌ، وَدِدْتُ أَنِّي نَجَوْتُ مِنْهَا كَفَافًا لاَ لِي وَلاَ عَلَىَّ لاَ أَتَحَمَّلُهَا حَيًّا وَمَيِّتًا‏

Narrated By 'Abdullah bin 'Umar : It was said to 'Umar, "Will you appoint your successor?" Umar said, "If I appoint a Caliph (as my successor) it is true that somebody who was better than I (i.e., Abu Bakr) did so, and if I leave the matter undecided, it is true that somebody who was better than I (i.e., Allah's Apostle) did so." On this, the people praised him. 'Umar said, "People are of two kinds: Either one who is keen to take over the Caliphate or one who is afraid of assuming such a responsibility. I wish I could be free from its responsibility in that I would receive neither reward nor retribution I won't bear the burden of the caliphate in my death as I do in my life."