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 is His slave and Messenger.
First of all, you should have sent to us the wording and text of the narrations as reported in the books of Hadeeth, but since you did not do so, we looked for them in the resources where they are most likely to be found and it appears that by the Hadeeth reported by Muslim, you refer to the Hadeeth of Umm Shareek who said: “I heard the Prophet saying: “The people would run away from the Dajjaal (i.e. the anti-Christ) seeking shelter in the mountains. Umm Shareek asked: “Where would be the Arabs on that day?” He said: “They would be small in number.” This Hadeeth means that the number of the Arabs will be small and that they will be unable to fight against the Dajjaal but it does not mean that most of them will follow him, even though we do not exonerate the non-Muslim Arabs from that. However, we do not know any area or country on which there is evidence that its people will follow the Dajjaal except what is reported by Muslim that the Prophet said: ''Seventy thousand of the Jews of Asfahaan (Isfahan) will follow him.”
Besides, Al-Mulla ‘Ali Al-Qaari said: ‘Verily, the people (meaning the believers) would run away from the Dajjaal until they reach the mountains, Umm Shareek said: “I said: O, Prophet of Allaah, where are the Arabs then? At-Teebi said: “…it means: if this is the case of the people, then where are the fighters in the Cause of Allaah who protect Islam and defend the Muslims against the aggression of the enemies of Allaah, and he said: ‘they (meaning the Arabs) are few (meaning on that day they will be so few that they will not be able to fight him).”
As regards the second Hadeeth, it might be that you refer to the following Hadeeth: “Three men will fight at the place where your treasure is, and each of them will be a son of a caliph, but none of them will get hold of it. Then black banners will appear from the east, and they will kill you in a way that has never been done to a nation before.” Thawbaan said: “Then he said something which I do not remember, and then he continued to say: “If you see him [i.e. the Mahdi], give him your allegiance even if you have to crawl on the ice (in order to do that).” [Ibn Maajah - Al-Qurbubi graded its chain of narrators authentic and Ibn Katheer wrote that its chain of narrators is strong and authentic].
This Hadeeth means that the Mahdi will be victorious over his opponents and that he will kill so many of them but the Hadeeth does not mention that he will totally abolish them and it did not mention the Arabs in particular but we have no doubt that Allaah will make him victorious over the Arabs who would oppose him, but many Arabs will be with him and he will be an Emir [leader] over them.
‘Abdullah Ibn Mas’ood narrated that the Prophet said: ''The world will not come to an end until a man from among my family, whose name matches my name, rules over the Arabs.” [Abu Daawood - Al-Albaani graded it Saheeh]
The scholars mentioned many probable explanations for the statement that he will rule over the Arabs and all of them indicate the status and the importance of the Arabs at that time.
Al-‘Atheem Abaadi said: "Ibn ‘Abdul Haadi As-Sindi said, in his commentary on Abu Daawood, that the Arabs were specifically mentioned here because they are the origin of Muslims and they are the most honorable among the Muslims.' Also, At-Teebi said that the non-Arabs were not mentioned but they are also meant because if he (Al-Mahdi) rules over the Arabs and they were united like one man with one hand (fighting their enemies), they would have overcome all other nations. This is also supported by a Hadeeth on the authority of Umm Salamah .” End quote.
Al-Mulla ‘Ali Al-Qaari’ said: “It could be said that the Arabs were mentioned because of their dominance at his (Al-Mahdi’s) time, or because of them being the most honorable or that what is mentioned implies another thing that is not mentioned and it means the Arabs and non-Arabs as well; like the saying of Allaah (which means): {…garments which protect you from the heat…} [Quran 16:81]; meaning and protects you from the cold as well. However, it is most likely that he just mentioned the Arabs because all of them will obey him unlike the non-Arabs who may differ about obeying him, and Allaah knows best.”
In any case, it cannot be understood from the Hadeeth that the Mahdi will kill any of the Muslims who are steadfast on the obedience of Allaah and who hold fast to the guidance of the Prophet whether they are Arabs or non-Arabs; as it is known that the Mahdi will fill out the earth with justice as in the Hadeeth of Ibn Mas’ood that the Prophet said: ''If there is only one day left in this world (for the Hour to come), Allaah will expand that day until He sends a man from me or from my family whose name matches my name and whose father’s name matches my father’s name. He will fill out the earth (i.e. this world) with justice and fairness just as it was initially filled with injustice and oppression.” [Abu Daawood, At-Tirmithi who graded it Hasan Saheeh]
As regards the Hadeeth of Bani Kulayb, then we hope that you will send us its wording so that we may be able to search its sources and speak about it.
Allaah Knows best.