Ja'far bin Abdullah bin Uthman said: I saw Muhammad bin 'Abbad bin Ja'far touching the Black Stone, kissing it, and placing his head upon it. I asked: What is this? He replied: I saw Sayyiduna 'Umar (may Allah be pleased with him) doing this and heard him say: I know that you are indeed a stone, and I do this only because I saw the Messenger of Allah (peace and blessings be upon him) doing it.
Hadith Referenceسنن دارمي / من كتاب المناسك / 1903
From this hadith, it is understood that touching (istilam) the Black Stone (Hajar al-Aswad), kissing it, and placing the head upon it are all established. All these actions are in following the Sunnah of the Leader of the Messengers (Sayyid al-Mursaleen) sallallahu alayhi wa sallam. The purpose is not to venerate the stone itself. The details of this have already been discussed in the explanation of hadith number (1877).