The subcontinent and valleys of the Hindu Kush remained unconquered by the Islamic armies until the 9th century, even though they had conquered the southern regions of Indus River valley such as Sind. Kabul fell to the army of Al-Ma'mun, the seventh Abbasid caliph, in 808 and the local king agreed to accept Islam and pay annual tributes to the caliph. However, states André Wink, inscriptional evidence suggests that the Kabul area near Hindu Kush had an early presence of Islam.