The ruling on whoever performs Hajj and he does not perform 'Umrah

Question :

I performed the obligatory Hajj and I did not perform Umrah with it. Is there any sin on me? And whoever performs "Umrah with his Hajj, is he obligated to perform 'Umrah another time?

Answer:

If the person performs Hajj and he has not performed 'Umrah before in his life after reaching puberty, then he should perform 'Umrah, whether he does it before the Hajj or after it. However, if he performed Hajj and he did not perform 'Umrah with it, then he should perform 'Umrah after the Hajj if he had not (ever) performed 'Umrah before. This is because Allâh obligated the Hajj and the 'Umrah. A number of Hadiths from the Prophet prove this. Therefore, it is obligatory upon the believer to perform it (the 'Umrah). If he combines Hajj and 'Umrah together as Qiran, there is no harm in that. This is done by him assuming Ihram for both of them together. He may also assume Ihram for 'Umrah, then he may add Hajj to it (later as At- Tamattu), and there is no harm in that. This suffices him. However, if he performs Hajj as a Mufrid by assuming Ihram for Hajj only from the Miqat, then remaining in his Ihram until he completes it, then he should perform an "Umrah afterwards from At-Tan'im or Al-Ji'ranah. This means that he performs the Umrah from the area that is not in the sacred precincts, outside of the Haram. Thus, he assumes Ihram from there, then he enters (the Haram of Makkah) and performs Tawaf and Sa'y, and he gets his hair cut or shaved off entirely. This is the 'Umrah as 'A'ishah performed it. For verily, when she came for Hajj in Ihram for 'Umrah, she got her menses near Makkah, so she was not able to perform Tawaf of the House (the Ka'bah) and complete her 'Umrah. Thus, the Messenger ordered her to assume Ihram for Hajj and to be a Qarin pilgrim. She did that and she completed her Hajj. Then, she requested permission from the Prophet to perform 'Umrah, because her female companions had performed 'Umrah by itself. Thus, he ordered her brother, 'Abdur-Rahman to take her to At-Tan'im so she could assume Ihram for 'Umrah from there. So, she went to At- Tan'im and assumed Ihram for 'Umrah, and she entered (Makkah), performed Tawaf and Say, and got her hair cut. This is a proof that whoever did not perform 'Umrah during his Hajj, it suffices him to assume Ihram from At-Tan'im and similar places that are outside of the Haram area. Such a person is not required to go out to the Miqat. In reference to whoever has performed 'Umrah and Hajj before, then he came again (to Makkah) and Allâh facilitates for him the performance of Hajj, he is not obligated to perform 'Umrah. He is sufficed by the previous 'Umrah, because 'Umrah is only obligatory once in a person's life, exactly like Hajj. Thus, the Hajj is (obligatory) once in a lifetime and so is the 'Umrah.

Source:
Ash-Shaykh Ibn Baz
Fatawa Islamiyah, Vol. 4 Pages 108-109-110