The Prophet has been quoted as saying, “I am the first who will reach the fountain of Hawdh al-Kawthar (located in Paradise). Some people will try to reach me, but they will not be able to. I will say, ‘O my Lord, they are my companions!’ Allah will answer, ‘You do not know what they have invented after you.’”
This hadith reflects that some of the companions did indeed err. Anyone who considers them all to be just would be disregarding this hadith. If all of the companions were considered to be just, then one must question as to why some of the companions who murdered Uthman b. al-Affan will go to Heaven? To say because they were companions would not justify entrance into Heaven.
Even more, anyone who considers them all to be just must also ponder why some of them revolted against Ali – the rightful ruler who had proven his loyalty to Allah, the Prophet, and Islam, and had partaken in the civil battles of Jamal, Siffeen, and Nahrawan, in which thousands of Muslims lost their lives, so will these companions who fought against him also be rewarded with Paradise?
 Sahih al-Bukhari; Sahih al-Muslim, Bab al-Hawdh, 7:65; Musnad Ahmad b. al-Hanbal, 5:333