When the Prophet ﷺ returned from Tabuk, the people asked him about the Hour. The Messenger of Allah ﷺ said, "A hundred years will not pass while a single soul now living on the earth remains alive."
لما رجع النبي ﷺ من تبوك سألوه عن الساعة، فقال رسول الله ﷺ: لا تأتي مائة سنة وعلى الأرض نفس منفوسة اليوم.
This was narrated by Muslim in Sahih Muslim, in the Book of the Virtues of the Companions (2539-219), through multiple chains from Abu Khalid Sulayman bin Hayan, from Dawud, from Abu Nadra, from Abu Saeed, and he mentioned it.Sheikh Islam bin Taymiya, may Allah have mercy on him, was asked about whether Khidr was still alive, and he said, "If Khidr were alive, he would have been obligated to come to the Prophet ﷺ, fight alongside him, and learn from him. The Prophet ﷺ said on the day of Badr, 'O Allah, if this small band is destroyed, You will not be worshiped on earth.' They numbered three hundred and thirteen men, known by their names, their fathers' names, and their tribes. So where was Khidr on that day?" See Majmu Fatawa (4/337).The hadiths reported about Khidr's continued life are numerous. Ibn Hajar collected them in his work devoted specifically to reports about Khidr, titled Al-Zahr al-Nadr fi Hal al-Khidr, and he explained their weakness. Ibn Jawzi likewise dealt with some of them in Al-Mawduat (1/30-322), as did Ibn Kathir in Al-Bidaya wal-Nihaya (2/180), and others, and they all explained their weakness and that none of them are authentically established from the Prophet ﷺ.As for whether Khidr was a prophet or merely a righteous saint, the context of the verses points to his prophethood in several respects.First, Allah's statement, "Then they found a servant from among Our servants to whom We had given mercy from Us and had taught him from Us a special knowledge" [Kahf 18:65]. The servant here is Khidr, whom Allah taught knowledge from Himself, just as He taught Adam the names of things.Second, Allah's statement, "Musa said to him, 'May I follow you on condition that you teach me from what you have been taught of sound judgment?'" [Kahf 18:66]. He said to him, meaning to Khidr, "May I follow you", and a prophet does not follow anyone in matters of religion except another prophet.Third, Khidr proceeded to kill the boy, and this could only have been by revelation to him from Allah, just as Ibrahim proceeded to slaughter his son after seeing it in a vision. Had Khidr not been a prophet, he would not have undertaken such an act merely on the basis of something occurring to his mind.Fourth, Khidr then explained to Musa the meaning behind those actions, clarifying to him the reality of his affair, saying, "And I did not do it upon my own command. That is the interpretation of what you could not have patience with" [Kahf 18:82], meaning that he did not do these things of his own accord, but rather did them by the command and revelation of Allah.For this reason Qurtubi said, "He is a prophet according to the majority, and the verse bears witness to this, because a prophet does not learn from someone beneath him in rank, and because judgment based on hidden, unseen matters is something only prophets are given access to."After fulfilling this task, Khidr died, just as any human being dies.