The ruling on whoever began 'Umrah and he did not complete it

Question :

Allah decreed that I go to perform 'Umrah during the past blessed month of Ramadhan. When I began performing Tawaf, I could not complete it due to the intense crowding. So, I left Makkah and went back to my city, and that was during the night of the 27th. I ask His Eminence, our Shaykh- - may Allâh protect him - about what is the consequence of this upon me, while knowing that I enjoy good health and all praise is due to Allâh. Please benefit me with an answer and may Allâh benefit you.

Answer:

Indeed you made a mistake in what you did. May Allâh pardon you and us. It was obligatory on you to complete the 'Umrah during another time other than the time of the crowding. This is due to Allâh's Statement:
"And complete the Hajj and the 'Umrah for Allah."

Indeed the scholars unanimously agree that it is obligatory upon whoever assumes Ihram for Hajj or 'Umrah to complete that and he may not remove his Ihram until after finishing the acts of 'Umrah and the acts of Hajj that make it permissible for him to remove his Ihram. The exception to this is the person who is stopped (from performing Hajj or 'Umrah) and the person who stipulates a condition if his condition actually occurs. Therefore, you must repent from what you did. Along with this you must also go to Makkah to complete the 'Umrah by performing Tawaf and Say, and shaving your hair or cutting it. You must also slaughter an animal, which is a seventh of a camel or a seventh of a cow, or one sheep, which means a two-year-old goat or a year-old sheep, if you had sex with your wife during the mentioned period of time. Along with this you must repent for what you did as mentioned previously. If you knew the ruling and that this act was not permissible for you, you must feed six poor people, giving each person half a Sa' of the food of the country, such as wheat or rice or other than them, or slaughter a sheep or fast three days. This is due to your wearing seamed garments and similar things, such as covering the head, using perfume, clipping the nails and shaving the head during the mentioned period. However, if you were ignorant, nothing is due on you of the mentioned ransom of atonement. This is due to the Statement of Allâh:
"Our Lord, do not take us to account (i.e., punish us) if we forget "or unintentionally err."

Indeed it has been authenticated from the Messenger of Allâh ﷺ that Allâh answered this supplication. This is also due to other evidences concerning this. And Allâh is the Giver of success.

Source:
Ash-Shaykh Ibn Baz
Fatawa Islamiyah, Vol. 4 Pages 284-285