Is a Muslim residing in Dar al-Harb (a non-Muslim territory) obligated to pay Zakat for past years if they return under Muslim authority?

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Zakat is obligatory for past years for a Muslim who embraced Islam while residing in Dar al-Harb and remained there for years without paying Zakat, or for the inhabitants of a town taken over by the Khawarij who withheld Zakat for years, once the Imam regains control. This position is the established doctrine of Malik and Al-Shafi'i. The evidence supporting this is that Zakat is a pillar of Islam, and it is not waived for someone outside the Imam's jurisdiction, similar to prayer and fasting.