Sahih Bukhari Volume 2, Book 25, Hadith 1606

حَدَّثَنَا سَعِيدُ بْنُ أَبِي مَرْيَمَ، أَخْبَرَنَا مُحَمَّدُ بْنُ جَعْفَرٍ، قَالَ أَخْبَرَنِي زَيْدُ بْنُ أَسْلَمَ، عَنْ أَبِيهِ، أَنَّ عُمَرَ بْنَ الْخَطَّابِ ـ رضى الله عنه ـ قَالَ لِلرُّكْنِ أَمَا وَاللَّهِ إِنِّي لأَعْلَمُ أَنَّكَ حَجَرٌ لاَ تَضُرُّ وَلاَ تَنْفَعُ، وَلَوْلاَ أَنِّي رَأَيْتُ النَّبِيَّ صلى الله عليه وسلم اسْتَلَمَكَ مَا اسْتَلَمْتُكَ‏.‏ فَاسْتَلَمَهُ، ثُمَّ قَالَ فَمَا لَنَا وَلِلرَّمَلِ إِنَّمَا كُنَّا رَاءَيْنَا بِهِ الْمُشْرِكِينَ، وَقَدْ أَهْلَكَهُمُ اللَّهُ‏.‏ ثُمَّ قَالَ شَىْءٌ صَنَعَهُ النَّبِيُّ صلى الله عليه وسلم فَلاَ نُحِبُّ أَنْ نَتْرُكَهُ‏

Narrated By Zaid bin Aslam : From his father who said: "Umar bin Al-Khattab addressed the Corner (Black Stone) saying, 'By Allah! I know that you are a stone and can neither benefit nor harm. Had I not seen the Prophet touching (and kissing) you, I would never have touched (and kissed) you.' Then he kissed it and said, 'There is no reason for us to do Ramal (in Tawaf) except that we wanted to show off before the pagans, and now Allah has destroyed them.' 'Umar added, '(Nevertheless), the Prophet did that and we do not want to leave it (i.e. Ramal).'