Bukhari

Hadith Commentary:
The word "Rafidi" is derived from "rafd." The researchers say that these Shia were named Rafidi because "they rejected (rafadu) Zayd ibn Ali ibn al-Husayn ibn Ali ibn Abi Talib for not disassociating himself from Abu Bakr and Umar."
The incident was that when Hazrat Zayd ibn Ali ibn Husayn (rahimahullah) came to Kufa and preached to the people, many pledged allegiance to him. However, a group among them said that unless you declare Abu Bakr and Umar to be evil, we will not pledge allegiance to you. Hazrat Zayd refused to accept this from them and remained steadfast upon the truth.
At that time, this group raised the slogan: "Nahnu narfudhuk" (We reject you).
From that time, this group became known as "Rafidi."
Hazrat Pir Jilani (rahimahullah) has severely condemned this group. In opposition to this group are the Khawarij, who rebelled against Hazrat Ali (radi Allahu anhu) and began to speak ill of him from the pulpit. Both factions are misguided. The moderation is with Ahl al-Sunnah, who honor all the Companions (radi Allahu anhum) and do not speak against any of them, entrusting their slips to Allah.
The elder mentioned in the narration, Ubaydah (rahimahullah), was a judge of Iraq. Hazrat Umar (radi Allahu anhu) held the opinion that the sale of an umm walad (a slave woman who has borne her master's child) is not permissible. Hazrat Ali (radi Allahu anhu) was of the view that the sale of an umm walad is permissible. Ubaydah submitted that during the time of Abu Bakr and Umar (radi Allahu anhuma), we used to give the fatwa of the impermissibility of selling an umm walad.
What is your ruling now? At that time, Hazrat Ali (radi Allahu anhu) said: "Continue to give the same ruling."

Hadith Commentary:
➊
The background of this hadith is stated to be that Ali (radi Allahu anhu) used to prohibit the buying and selling of an umm walad (a slave woman who has borne a child to her master). When he saw that people were engaging in this transaction, he retracted his statement, saying that his opinion was causing disagreement among the people, which he did not like. He preferred to act upon the decisions of the two Shaykhs (Abu Bakr and Umar, radi Allahu anhuma), as this would maintain unity and consensus. Therefore, he abandoned his own opinion so that people would not fall into tribulation.

➋
The meaning of Ibn Sirin (rahimahullah) is that the statements which the Shia present from Ali (radi Allahu anhu) in opposition to the two Shaykhs have no validity; rather, all of them are false and fabricated.

(Fath al-Bari: 7/94)

➌
This hadith demonstrates the virtue of Ali (radi Allahu anhu) in that he abandoned his own opinion for the sake of maintaining unity.

➍
Ali (radi Allahu anhu) was martyred by the accursed Ibn Muljam in Ramadan of the year 40 AH, corresponding to January 661 CE.

Inna lillahi wa inna ilayhi raji'un.

➎
Among the wonders of Allah’s power is that the order of the caliphate occurred in such a way that the person who was genealogically closest to the Messenger of Allah (sallallahu alayhi wa sallam) received the caliphate later, while the person who was more distant received the caliphate earlier.

And Allah knows best.