Translation
(63) Merits of the Helpers in Madinah (Ansaar)
كتاب مناقب الأنصار
(35) Chapter: The conversion ‘Umar رضي الله عنه to Islam
(35) باب إِسْلاَمِ عُمَرَ بْنِ الْخَطَّابِ رضى الله عنه
Sahih al-Bukhari 3867 

Narrated Qais:

I heard Sa`id bin Zaid saying to the people, "If you but saw me and `Umar's sister tied and forced by `Umar to leave Islam while he was not yet a Muslim. And if the mountain of Uhud could move from its place for the evil which you people have done to `Uthman, it would have the right to do that."

حَدَّثَنِي مُحَمَّدُ بْنُ الْمُثَنَّى، حَدَّثَنَا يَحْيَى، حَدَّثَنَا إِسْمَاعِيلُ، حَدَّثَنَا قَيْسٌ، قَالَ سَمِعْتُ سَعِيدَ بْنَ زَيْدٍ، يَقُولُ لِلْقَوْمِ لَوْ رَأَيْتُنِي مُوثِقِي عُمَرُ عَلَى الإِسْلاَمِ أَنَا وَأُخْتُهُ وَمَا أَسْلَمَ، وَلَوْ أَنَّ أُحُدًا انْقَضَّ لِمَا صَنَعْتُمْ، بِعُثْمَانَ لَكَانَ مَحْقُوقًا أَنْ يَنْقَضَّ‏.‏
Reference : Sahih al-Bukhari 3867
In-book reference : Book 63, Hadith 92
USC-MSA web (English) reference : Vol. 5, Book 58, Hadith 207
  (deprecated numbering scheme)