I used to teach Qur'an to 'Abdur-Rahman bin Auf. When Umar performed his last Hajj, 'Abdur-Rahman said (to me) at Mina, "Would that you had seen Chief of the believers today! A man came to him and said, "So-and-so has said, "If Chief of the Believers died, we will give the oath of allegiance to such-and-such person,' 'Umar said, 'I will get up tonight and warn those who want to usurp the people's rights.' I said, 'Do not do so, for the season (of Hajj) gathers the riffraff mob who will form the majority of your audience, and I am afraid that they will not understand (the meaning of) your saying properly and may spread (an incorrect statement) everywhere. You should wait till we reach Medina, the place of migration and the place of the Sunna (the Prophet's Traditions). There you will meet the companions of Messenger of Allah ﷺ from the Muhajirin and the Ansar who will understand your statement and place it in its proper position' 'Umar said, 'By Allah, I shall do so the first time I stand (to address the people) in Medina.' When we reached Medina, 'Umar (in a Friday Khutba-sermon) said, "No doubt, Allah sent Muhammad with the Truth and revealed to him the Book (Quran), and among what was revealed, was the Verse of Ar-Rajm (stoning adulterers to death).'" (See Hadith No. 817,Vol. 8)  

عَبْدُ الرَّحْمَنِ بِمِنًى لَوْ شَهِدْتَ أَمِيرَ الْمُؤْمِنِينَ أَتَاهُ رَجُلٌ قَالَ إِنَّ فُلاَنًا يَقُولُ لَوْ مَاتَ أَمِيرُ الْمُؤْمِنِينَ لَبَايَعْنَا فُلاَنًا فَقَالَ عُمَرُ لأَقُومَنَّ الْعَشِيَّةَ فَأُحَذِّرَ هَؤُلاَءِ الرَّهْطَ الَّذِينَ يُرِيدُونَ أَنْ يَغْصِبُوهُمْ قُلْتُ لاَ تَفْعَلْ فَإِنَّ الْمَوْسِمَ يَجْمَعُ رَعَاعَ النَّاسِ يَغْلِبُونَ عَلَى مَجْلِسِكَ فَأَخَافُ أَنْ لاَ يُنْزِلُوهَا عَلَى وَجْهِهَا فَيُطِيرُ بِهَا كُلُّ مُطِيرٍ فَأَمْهِلْ حَتَّى تَقْدَمَ الْمَدِينَةَ دَارَ الْهِجْرَةِ وَدَارَ السُّنَّةِ فَتَخْلُصُ بِأَصْحَابِ رَسُولِ اللَّهِ ﷺ مِنَ الْمُهَاجِرِينَ وَالأَنْصَارِ فَيَحْفَظُوا مَقَالَتَكَ وَيُنَزِّلُوهَا عَلَى وَجْهِهَا فَقَالَ وَاللَّهِ لأَقُومَنَّ بِهِ فِي أَوَّلِ مَقَامٍ أَقُومُهُ بِالْمَدِينَةِ قَالَ ابْنُ عَبَّاسٍ فَقَدِمْنَا الْمَدِينَةَ فَقَالَ إِنَّ اللَّهَ بَعَثَ مُحَمَّدًا ﷺ بِالْحَقِّ وَأَنْزَلَ عَلَيْهِ الْكِتَابَ فَكَانَ فِيمَا أُنْزِلَ آيَةُ الرَّجْمِ