Sunan an-Nasa'i, Volume 3, Book 24, Hadith 2940 (DarusSalam) ⓘ

It was narrated Abbas bin Rabiah said: "I saw Umar coming to the Stone and saying: 'I know that you are just a stone; had I not seen the Messenger of Allah kiss you I would not have kissed you.' Then he came close to it and kissed it." (Sahih) Chpater 148. How to Kiss It

أَخْبَرَنَا إِسْحَاقُ بْنُ إِبْرَاهِيمَ، قَالَ أَنْبَأَنَا عِيسَى بْنُ يُونُسَ، وَجَرِيرٌ، عَنِ الأَعْمَشِ، عَنْ إِبْرَاهِيمَ، عَنْ عَابِسِ بْنِ رَبِيعَةَ، قَالَ رَأَيْتُ عُمَرَ جَاءَ إِلَى الْحَجَرِ فَقَالَ إِنِّي لأَعْلَمُ أَنَّكَ حَجَرٌ وَلَوْلاَ أَنِّي رَأَيْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُبِّلُكَ مَا قَبَّلْتُكَ ‏.‏ ثُمَّ دَنَا مِنْهُ فَقَبَّلَهُ ‏.‏