Hadith #2950 (Sahih Muslim)
Book: The Book of Pilgrimage
Narrator(s): Abis bin Rabi'a al-Nakha'i عابس بن ربيعة النخعي
Grade: Sahih

I saw ‘Umar (Allah’be pleased with him) kissing the Stone and saying: I am kissing you and I know that you are a stone. And if I had not seen Allah’s Messenger (ﷺ) kissing you, I would not have kissed you.

Source: https://parallelquran.com/hadith/sahih-muslim-2950/