Sahih al-Bukhari 6942
Narrated Qais:
I heard Sa`id bin Zaid saying, "I have seen myself tied and forced by `Umar to leave Islam (Before 
`Umar himself embraced Islam). And if the mountain of Uhud were to collapse for the evil which you 
people had done to `Uthman, then Uhud would have the right to do so." (See Hadith No. 202, Vol. 5)
حَدَّثَنَا سَعِيدُ بْنُ سُلَيْمَانَ، حَدَّثَنَا عَبَّادٌ، عَنْ إِسْمَاعِيلَ، سَمِعْتُ قَيْسًا، سَمِعْتُ سَعِيدَ بْنَ زَيْدٍ، يَقُولُ لَقَدْ رَأَيْتُنِي وَإِنَّ عُمَرَ مُوثِقِي عَلَى الإِسْلاَمِ، وَلَوِ انْقَضَّ أُحُدٌ مِمَّا فَعَلْتُمْ بِعُثْمَانَ كَانَ مَحْقُوقًا أَنْ يَنْقَضَّ‏.‏