Kindly explain the Hadeeth that I couldn't understand when the Prophet Muhammad (SAW) said, "My sahaba will be taken to the fire [of hell], whereupon I shall plead: "O Lord! But these are my sahaba!" It will be said to me, "You do not know what they brought forth after you." I will say, "Then perdition should be the lot of all those who altered after me." (Sahih Bukhari, Vol. 7, p. 209, in a chapter dealing with the Pool [of al-Kawthar]) What about Shiites? Are they Muslims who need clarification or is there any Shia group that follows true Islam?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

Anas narrated that the Prophet said: "Some people from my Companions will come to my Hawdh (Cistern) and I will recognize them. Then, they will be driven away from it, and I will say: “They are my Companions.” It will be said, “You do not know what they innovated (in religion) after you were gone.” [Al-Bukhari]

In the narration of Abu Sa’eed Al-Khudri the following addition was reported: “…I would say: “They are from me.” It will be said, “You do not know what they innovated (in religion) after you were gone.” Then I would say: “Away with them, away with them for those who changed (in religion) after I was gone.” [This Hadeeth was also reported by Muslim, Ahmad, Abu Daawood, At-Tirmithi, Ibn Maajah and An-Nasaa’i with different wordings]

The scholars elaborated on the above Hadeeth and similar Ahaadeeth, and some of them understood it to mean apostasy. For instance Ibn Al-Jawzi said in his book Kashf Al-Mushkil Min Ahaadeeth As-Saheehayn, “It appears that some became hypocrites in the era of the Prophet, sallallaahu ‘alayhi wa sallam, and some became non-Muslims after he died. Abu Bakr ibn Muqsim said, 'They – and Allaah knows best – are those who came to him from tribe of Bani Haneefah and he saw them and knew them but afterwards they apostatized with Musaylimah and died as non-Muslims, but none of the Companions of the Prophet died as a non-Muslim.'”  Besides, Ibn Hajar said, “Al-Farbari said, 'It was said that Abu ‘Abdullaah Al-Bukhari quoted Qabeesah as saying, 'They are those who apostatized during the era of Abu Bakr and Abu Bakr fought against them'", meaning until they were killed and died as non-Muslims.

Ibn Hajar also quoted Al-Khattaabi as saying, “None of the Companions apostatized; rather, those who apostatized were a group from the rude Bedouins who did not support the religion and this does not necessitate degrading the famous Companions. What proves this is that the Prophet, sallallaahu ‘alayhi wa sallam, said what means that those Companions were small in numbers."

Some other scholars understood this Hadeeth to refer to some disobedient persons among the Companions . Al-‘Ayni said, “The statement of the Prophet, sallallaahu ‘alayhi wa sallam: “… what they innovated (in religion) after you were gone…” means the acts of disobedience committed by some Companions that necessitate preventing (them) from drinking from the Prophet’s Hawdh.”

Allaah Knows best.