Narrated Hudhaifah [may Allah be pleased with him]:
"We were sitting with the Prophet (ﷺ) and he said: 'I do not know how long I will be with you, so stick to the two after me,' and he signaled towards Abu Bakr and 'Umar." (ES)
English reference (ES): Vol. 1, Book 46, Hadith 3663 (ES)
Arabic reference (ES): Book 49, Hadith 4025 (ES)