"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 (Using translation from Nasāʾī 2937)
إِنِّي أَعْلَمُ أَنَّكَ حَجَرٌ «وَلَوْلَا أَنِّي رَأَيْتُ رَسُولَ اللهِ ﷺ يُقَبِّلُكَ مَا قَبَّلْتُكَ ثُمَّ دَنَا مِنْهُ فَقَبَّلَهُ»