Abdur Razaq San'ani (Died 211 AH) narrated a lengthy narration in which Abbas and Ali Ibn Abi Talib (as) went to 'Umar to resolve a dispute upon which 'Umar told them like this :
.....فلما قبض رسول الله صلى الله عليه وسلم قال أبو بكر: أنا ولي رسول الله صلى الله عليه وسلم بعده، أعمل فيه بما كان يعمل رسول الله صلى الله عليه وسلم فيها. ثم أقبل على علي والعباس فقال: وأنتما تزعمان أنه فيها ظالم فاجر والله يعلم أنه فيها صادق بار تابع للحق، ثم وليتها بعد أبي بكر سنتين من إمارتي، فعملت فيها بما عمل رسول الله صلى الله عليه وسلم وأبو بكر وأنتما تزعمان أني فيها ظالم فاجر،.....
.....When Messenger of Allah (swt) died Abu Bakr said : I am Wali (Sucessor) of Messenger of Allah (swt) after him, I will do the way he used to do. Then Umar faced towrads Ali and Umar and told them : You both used to believe him (Abu Bakr) to be Oppressor and Sinfull. I swear by Allah, He was truthfull and follower of Right path in that and After Abu Bakr i became Wali (Sucessor) for 2 years and i did the same what Prophet (ﷺ) and Abu Bakr used to do and you two believe me to be a Oppressor and Sinfull.....
Now the same narration is quoted by Abu Bakr Marwadhi (Died 292 AH) from Abdur Razaq San'ani via an intermediate narrator and wee see the opinion of Ali and Abbas about Abu Bakr and Umar has been distorted to by erasing these words ( ظالمٌ فاجرٌ - Oppressors and Sinfull ).
Musnad Abu Bakr - Mardwadhi // Page 32 - 34 // Number 2 // Edn. Maktaba Islami Riyadh Saudi.
Note : This edition of Musnad Abu Bakr has been investigated by Sh'oaib Al-Arna'ut and he has used the manuscript of Maktaba Dhahiriyyah Library Damascus Syria and you can see in this edition he has used other books to complete any deficant narration while in above narration he was so ashamed to quote the actual full narration from Musnad Abdur Razaq that he only wrote some dots and in actual Manuscript there are no dots.