Jami` at-Tirmidhi 3150
جامع الترمذي#3150SahihNarrated Ibn 'Abbas:that Ubayy bin Ka'b narrated that the Prophet (ﷺ) said: "The boy that Al-Khidr killed was destined to be a disbeliever the day he was created
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Ahmad Muhammad ShakirSahih
Al-AlbaniSahih
Bashar Awad MaaroufHasan Sahih
Zubair Ali ZaiSahih Muslim
In-book reference: 47:202