This article argues that collaboration between religion and culture is salient feature of the life of Muslims in Padangsidempuan. This good compromise helps tradition become an effective mean of spreading religion. The inclusive relationship between religion and culture creates dynamic and harmonious integration. Islamic law benefits from this because such a pattern enables the law to be integrated and accepted by the society culturally. Under the principle of “hombaradatdohotibadat”, Islamic law is received by adat (culture or tradition), even in the form of worship. This principle is tangible evidence that the local tradition of BatakAngkola contains and accommodates Islamic legal elements, such as the tradition of “martolong”.