Muwatta Malik, Book 20, Hadith 113 (USC-MSA) ⓘ

Yahya related to me from Malik that he had heard that when the Messenger of Allah, may Allah bless him and grant him peace, had finished his tawaf of the House, prayed two rakas, and wanted to go to Safa and Marwa, he would salute the corner of the Black Stone before he left.

حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ إِذَا قَضَى طَوَافَهُ بِالْبَيْتِ وَرَكَعَ الرَّكْعَتَيْنِ وَأَرَادَ أَنْ يَخْرُجَ إِلَى الصَّفَا وَالْمَرْوَةِ اسْتَلَمَ الرُّكْنَ الأَسْوَدَ قَبْلَ أَنْ يَخْرُجَ ‏.‏