According to reliable chain of narrators, it is narrated from Bukayr that Imam as-Sadiq asked him, “Do you know what the Black Stone was originally?” “No,” said Bukayr. Imam said, “It was a Great Angel of Allah. When Allah took the covenant from angels, it was the first to believe and accepted Allah; the Black Stone is the same angel. Allah made him His trustee over other creatures and made them perform hajj near it every year.
When Adam committed the mistake and neglected the covenant that was taken from him and his children, for Muhammad and his Legatee, he landed on the Earth, puzzled and perplexed. When his repentance was accepted, Allah sent this same angel in the form of a pure white shinning pearl to Adam from heaven when he was in India. Adam saw the Angel and was enchanted by him but he thought it was a pearl. Allah made it speak. It said, ‘O Adam! Do you know me?’ He said, ‘No.’ It said, ‘You do know me but Satan has overpowered you made your heart forget Allah.’ Saying this he regained the form that Adam seen in heaven. Then he asked Adam of his covenant with Allah. Adam moved towards him, then suddenly remembered the covenant and began to weep. As a mark of respect to the covenant and renewing of oath, he kissed the Angel.
Allah again made it into a white glowing pearl. Due to its importance, Adam carried it on his shoulders. When he used to get tired, Archangel Gabriel used to carried it, until they reached Makkah. Adam always showed a great regard for it and renewed his oath day and night. When Allah sent Archangel Gabriel to construct the Ka‘bah, he came down between the Rukn, Hajar and door and appeared Adam when he was renewing his covenant. Therefore, the covenant was entrusted to the Angel at this very place. He fixed the Hajar to this pillar. Archangel Gabriel took Adam from Ka‘bah to Mt. Safa and Hawwa’ to Mt. Marwa. Adam praised and glorified Allah.
Therefore it is recommended for all to face the Hajar from Mt. Safa and recite Allahu Akbar.”