Musnad Ahmad 2:231

Rawh narrated to us, Ibn Jurayj narrated to us, Sulayman ibn ‘Atiq informed me, from ‘Abdullah ibn Babiyah, from some of the sons of Ya’la, from Ya’la ibn Umayyah, who said: I performed Tawaf with ‘Umar ibn al-Khattab, and he touched the Corner (the Black Stone). Ya’la said: I was on the side closest to the House. When I reached the western corner that is next to the Black (Stone), I pulled his hand so that he would touch it. He said: "What is the matter with you?" I said: "Will you not touch it?" He said: "Did you not perform Tawaf with the Messenger of Allah, peace and blessings of Allah be upon him?" I said: "Yes." He said: "Did you see him touch these two western corners?" I said: "No." He said: "Is there not a good example for you in him?" I said: "Yes." He said: "Then move on."