The Prophet ﷺ said, "There will come rulers who lie and oppress. Whoever believes their lies and assists them in their oppression is not of me, nor am I of him, and he will not come to me at the Pond. But whoever does not believe their lies and does not assist them in their oppression is of me, and I am of him, and he will come to me at the Pond."
عن النبي ﷺ قال: إنها ستكون أمراء يكذبون ويظلمون، فمن صدقهم بكذبهم، وأعانهم على ظلمهم، فليس مني ولست منه، ولا يرد علي الحوض، ومن لم يصدقهم بكذبهم، ولم يعنهم على ظلمهم فهو مني وأنا منه، وسيرد علي الحوض.
Imam Ahmad (23260) and Bazzar (2834) both narrated it through the hadith of Ismail bin Ulaya, from Yunus bin Ubayd, from Humayd bin Hilal, or from someone else, from Rabi bin Harash, from Huzaifa, who related something similar. Except that in Bazzar's version it reads "from Rabi or someone else," placing the doubt on Rabi rather than on Humayd. The correct view is that the doubt lies with Humayd, because Bazzar (2833) and Tabarani in al-Awsat (8486) narrated it through Sahl bin Aslam Adawi, from Yunus bin Ubayd, with his chain, without any doubt at all. Bazzar said, "Sahl bin Aslam did not doubt it."As for what is narrated from Ibn Umar, attributed to the Prophet, "There will be rulers over you who will command you to do what they themselves do not do. Whoever believes their lies and helps them in their wrongdoing is not from me, and I am not from him, and he will never come to me at the Pool," this is daif. Imam Ahmad (5702) and Bazzar, in Kashf Astar (1608), both narrated it through Ala bin Musayab, from Ibrahim bin Qais, from Nafi, from Ibn Umar, who related it. Ibrahim bin Qais is Ibrahim bin Ismail bin Qais, the freedman of Banu Hashim. Abu Hatim graded him daif, while Ibn Hibban graded him reliable, and Haythami cited this as the reason for its weakness in Majma (5/247).It also contains the hadith of Khabab bin Arat. Imam Ahmad (21074) and Tabarani (2627) narrated it, and Ibn Hibban (284) and Hakim (1/78) both graded it sahih, all through Hatim bin Abu Saghira Abu Yunus Qushayri, from Simak bin Harb, from Abdullah bin Khabab, from his father Khabab, who related the hadith with wording close to it. Hakim said, "It is sahih according to the standard of Muslim." However, they failed to notice that there is a break in the chain between Simak bin Harb and Abdullah bin Khabab, for Abdullah bin Ahmad said, "I asked my father, 'Did Simak bin Harb hear from Abdullah bin Khabab?'" He said, "No." Alai mentioned this in Jami Tahsil, in the biography of Simak bin Harb (265), and Mizzi said in his Tahdhib, in the biography of Abdullah bin Khabab, "Simak bin Harb narrated from him but did not meet him."It also contains the hadith of Numan bin Bashir. Imam Ahmad (18353) narrated it, but it contains an unnamed man, and it makes no mention of the Pool. And the hadith of Abu Saeed Khudri. Imam Ahmad (11192) narrated it, but it contains an unknown man, and it too makes no mention of the Pool.Among the important points, Qurtubi, may Allah Most High have mercy on him, said, "Among the things that every accountable person must know and affirm is that Allah Most High singled out His Prophet Muhammad ﷺ with Kawthar, which is the Pool explicitly named, described, along with its drink and its vessels, in the many well-known sahih hadiths, the sum of which produces certain knowledge and the certainty that comes from being transmitted through many corroborating chains. This was narrated from the Prophet ﷺ by more than thirty of his companions. More than twenty of them are found in Sahihayn, and the rest are in other collections whose transmission has been reliably established and whose narration is well known. It was then narrated from the companions by the successors, their equals, and these hadiths, as the generations succeeded one another and the narrators multiplied across every region, continued to attract the determined efforts of transmitters, who narrated them, preserved them in the major compilations, and recorded them in writing, until this reached us, and Allah's proof was thereby established against us. It is therefore obligatory upon us to believe in this and affirm it, just as the early generations agreed upon it, along with the people of the sunnah among the later generations. A group of innovators denied it, diverted it from its apparent meaning, and went to excess in reinterpreting it, without any rational or customary necessity compelling them to deny its apparent meaning, and without any textual or transmitted dispute calling for its reinterpretation. Their reinterpretation is therefore a distortion stemming from feeble reasoning, through which they broke the consensus of the early generations and departed from the doctrine of the later scholars." End of quote, from Mufhim Lima Ashkala min Talkhis Kitab Muslim (6/90).As for his statement that "Kawthar is the Pool," the correct view is that Kawthar is a river in Paradise that flows into the Pool, as is established in the sahih hadiths. Ibn Hajar, in Fath al-Bari (11/467), quoted the aforementioned words of Qurtubi, except that the mention of "Kawthar" was dropped from it, so the statement became, "He singled out His Prophet Muhammad ﷺ with the Pool explicitly named... etc." Ibn Hajar then said, "The Kharijites and some of the Mutazilites denied it, and among those who used to deny it was Ubaydullah bin Ziyad, one of the governors of Iraq under Muawiya and his son."I say, Ubaydullah bin Ziyad later came to believe in the Pool when he heard the words of Abu Sabra, and said, "I have not heard any account about the Pool more firmly established than this," so he believed it, took the written page, and kept it in his possession. The full hadith, along with its sourcing, has already been given earlier.Regarding his saying "asayhabi," this is in the diminutive form, while "ashabi" is in the non-diminutive form, and they fall into two categories. The first are sinners who turned away from the right path, not from Islam itself, and who replaced righteous deeds with evil ones. These will enter Paradise through the intercession of the Prophet and will not remain in the Fire forever. The second are those who truly reverted to disbelief, meaning the companions of Musaylima the Liar who apostatized after the death of the Prophet ﷺ, whom Abu Bakr fought, along with some of the rough Bedouin Arabs.There is nothing in these hadiths that provides evidence for the Shia's claim that all the companions apostatized except a small few, for reality itself refutes them, since none of the companions apostatized. Rather, it was only some of the rough Bedouin Arabs and the companions of Musaylima the Liar who apostatized.