Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) used to say that a Muhrim (one in the state of Ihram) who is prevented by any obstacle should not exit from the Ihram of Hajj or Umrah without performing the Tawaf of the House of Allah. However, if he is prevented by an enemy, then he may exit from Ihram at that very place. And whoever is prevented by a general illness or the like should remain in the state of Ihram until he performs the Tawaf of the House of Allah, then he becomes lawful from his Umrah.
Hadith Referenceالسنن المأثورة / باب ما جاء في فدية الأذى / 461