Sunan an-Nasa'i, hadith 2952

أَخْبَرَنَا عُبَيْدُ اللَّهِ بْنُ سَعِيدٍ، قَالَ حَدَّثَنَا يَحْيَى، عَنْ عُبَيْدِ اللَّهِ، عَنْ نَافِعٍ، قَالَ قَالَ عَبْدُ اللَّهِ رَضِيَ اللَّهُ عَنْهُ مَا تَرَكْتُ اسْتِلاَمَ هَذَيْنِ الرُّكْنَيْنِ مُنْذُ رَأَيْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَسْتَلِمُهُمَا الْيَمَانِيَ وَالْحَجَرَ فِي شِدَّةٍ وَلاَ رَخَاءٍ ‏.‏

It was narrated that Nafi said:"Abdullah, may Allah be pleased with him, said: "I have not failed to touch these two corners since I saw the Messenger of Allah touching them, the Yemeni Corner and Black Stone, either when it is difficult or when it is easy