Sayyiduna Ibrahim (may Allah have mercy on him) says: "If a person from the people of Sawad (Iraq) accepts Islam and remains on his land, then kharaj (land tax) is taken from him, and if he leaves the land, then the kharaj ends for him."
Hadith Referenceسنن سعید بن منصور / كتاب الجهاد / 3769
Hadith Takhrij«أخرجه سعيد بن منصور فى «سننه» ترقيم الدرالسلفية برقم:، 2592، وابن أبى شيبة فى «مصنفه» برقم: 21954، 33617»