The obligation of Umrah is one of the well-known points of scholarly difference among the four schools of Sunni Islamic jurisprudence, and both positions are supported by legitimate evidence. The Shafi'i and Hanbali schools hold that Umrah is wajib (fardhu or wajib) once in a lifetime for every Muslim who meets the conditions of ability, similar to Haji. Their primary evidence is Al-Al-Quranic verse: 'And complete the Haji and Umrah for Allah' (2:196), which they interpret as a command to perform both Haji and Umrah. They also cite the hadith in which Nabi was asked about Umrah: 'Is it wajib?' and he replied, 'No, but if you perform Umrah it is better for you,' though the Shafi'i scholars note some chains of this narration are weak, and they rely on stronger evidence for the obligation.
The Hanafi and Maliki schools hold that Umrah is a strongly sunnah Sunnah (sunnah mu'akkadah) but not wajib. Imam Abu Hanifah and Imam Malik both interpreted Al-Al-Quranic verse 'Complete the Haji and Umrah for Allah' as referring to completing the rites once you have begun them (i.e., if you start Haji or Umrah, you must finish them), rather than as a command to initiate both. They also cite the hadith of Jabir in which Nabi was asked whether Umrah is wajib and he said it is not (reported by al-Tirmidhi), along with the fact that Nabi only performed Umrah when it coincided with his travels for Haji or other purposes, never making a journey solely for Umrah as a standalone obligation.
In practical terms, this scholarly difference has limited real-world impact because all four schools agree that performing Umrah is highly meritorious and strongly encouraged. Nabi (shallallahu alaihi wa sallam) said, 'Umrah to Umrah is an expiation for the sins between them.' Even the Hanafi and Maliki scholars who classify it as Sunnah consider it one of the most highly sunnah acts of worship in Islam. Whether one follows the view that it is wajib or the view that it is Sunnah, the recommendation is the same: if you have the means and ability, you should perform Umrah at least once in your lifetime, and repeating it is a source of great reward.