The shia believe that Hazrat Ali was the rightful successor of the Prophet and was appointed as the Caliph by Hazrat Muhammad at the event of Ghadeer. See link below.
Based on this, they believe that the three caliphs were unjustified in their actions of taking up (or accepting) the caliphate.
The shia beliefs strictly follows sayings and rulings of Hazrat Ali after Hazrat Muhammad as they believe Ali was the religious authority after Hazrat Muhammad and they believe he was the first Imam ( a designation that they believe is a form of caliphate appointed by God).
So its natural that they would not consider any person in Islamic history as rightful if they find that person stood up against Ali. In presence of many such events and personalities they favour Ali in all the instance and show disassociation with others.
Some shia go to extremes because some events have been reported in history that disturb them. Some of these are:
The shia have great respect for the Prophet and his family and due to all above events they disassociate themselves from the people who were against the Prophet's family.
However their Ulema do not approve of use of abusive language for these personalities for the sake of unity of the Muslim Ummah. However the practice of 'disassociation' with these personalities has the approval from the Ulema as well.
Comment in the aboveAll the above is a kind of history that its authentication is not completely validated. It enough to state two facts:HAZRAT USMAN was the third khalipha.
Hazrat Ume Kulsoom & Hazrat Ruqaiyya.
Mysara
Affan
Urwa Binte kariez .
Because two daughters of prophet muhammad got married to hazrat usman ..zun noor..
Hazrat Abu Bakr, Hazrat Umar Farooq, Hazrat Usman Ghani, Hazrat Ali (May Allah be pleased with them all).
Hazrat Usman (Ral)
The third Righteous Caliph Hazrat Usman Ghani RAU. He is also known as jami-ul-Qur'an.
The Muslims are bound to follow the example of beloved Prophet Hazrat Muhammad (SAW), as he is the best example.
they were 10 in numbers but i am missing the name some of them, Hazrat Abu Baker Siddique,Hazrat Umer,Hazrat Usman,Hazrat Ali,Hizrat Billal,Hazrat Salman Farsi, Etc...
Mutual differences after the assaisination of the Third Rightful Caliph Hazrat Usman (RAU).