Shaykh Muhammad ibn ‘Uthaymeen (may Allaah have mercy on him) said:
“The one who starts his tawaaf from the door of the Ka’bah and completes it on this basis is not regarded as having completed tawaaf, because Allaah says (interpretation of the meaning):
“and circumambulate the Ancient House (the Ka‘bah at Makkah)”
The Prophet (peace and blessings of Allaah be upon him) started his tawaaf at the Black Stone and said to the people: “Learn from me your rituals (of Hajj).” Narrated by Muslim, 1297.
If he starts tawaaf at the door of the Ka’bah, or not in line with the Black Stone, even if he is only off by a little, then this first circuit is invalid, because it is not complete. He has to repeat it if he remembers shortly afterwards, otherwise he has to do the whole tawaaf over again, starting in line with the Black Stone.
A line has been placed on the ground in line with the Black Stone, extending to the edge of the area for tawaaf, as a sign of where to start and end tawaaf. Since this line was drawn, people’s mistakes in doing tawaaf have become fewer, but there are still a few ignorant people. Whatever the case, people have to pay attention to this mistake, lest they fall into the serious danger of their tawaaf not being complete.
See: Daleel al-Akhta’ allati yaqa’a fiha al-Haaj wa’l-Mu’tamir (mistakes made by pilgrims performing Hajj and ‘Umrah).