No one questioned the Prophet ﷺ about him more than I did. He said, "He will not harm you."I said, "They say he will have a river with him, and such and such."He replied, "He is more insignificant before Allah than that."
حدثنا محمد بن جعفر حدثنا شعبة عن إسماعيل عن قيس
ما سأل أحد النبي ﷺ أكثر مما سألت أنا عنه فقال إنه لا يضرك قال قلت إنهم يقولون معه نهر وكذا وكذا قال هو أهون على الله من ذاك
Its isnad is sahih, its narrators are trustworthy and well known. Bukhari narrated the hadith in 13/89, no. 7122, in Fath al-Bari, in the chapters on tribulations, mention of Dajjal, and Muslim in 4/2257-2258, in the chapters on tribulations. The pronoun refers back.