are common practice today. For example Qawwali was originally a form of Sufi devotional singing popular in the Indian subcontinent, and is now usually performed at dargahs. Sufi saint Amir Khusrau is said to have infused Persian, Arabic Turkish and Indian classical melodic styles to create the genre in the 13th century. The songs are classified into hamd, na'at, manqabat, marsiya or ghazal, among others. Nowadays, the songs last for about 15 to 30 minutes, are performed by a group of singers, and instruments including the harmonium, tabla and dholak are used. Pakistani singing maestro Nusrat Fateh Ali Khan is credited with popularizing qawwali all over the world. Saints Walī (, plural ) is an Arabic word whose literal meanings include "custodian", "protector", "helper", and "friend." In the vernacular, it is most commonly used by Muslims to indicate an Islamic saint, otherwise referred to by the more literal "friend of God." In the traditional Islamic understanding of saints, the saint is portrayed as someone "marked by [special] divine favor ... [and] holiness", and who is specifically "chosen by God and endowed with exceptional gifts, such as the ability to work miracles." The doctrine of saints was articulated by Islamic scholars very early on in Muslim history, and particular verses of the Quran and certain hadith were interpreted by early Muslim thinkers as "documentary evidence" of the existence of saints. Since the first Muslim hagiographies were written during the period when Sufism began its rapid expansion, many of the figures who later came to be regarded as the major saints in Sunni Islam were the early Sufi mystics, like Hasan of Basra (d. 728), Farqad Sabakhi (d. 729), Dawud Tai (d. 777-81) Rabi'a al-'Adawiyya (d. 801), Maruf Karkhi (d. 815), and Junayd of Baghdad (d. 910). From the twelfth to the fourteenth century, "the general veneration of saints, among both people and sovereigns, reached its definitive form with the organization of Sufism ... into orders or brotherhoods." In the common expressions of Islamic piety of this period, the saint was understood to be "a contemplative whose state of spiritual perfection ... [found] permanent expression in the teaching bequeathed to his disciples." Visitation In popular Sufism (i.e. devotional practices that have achieved currency in world cultures through Sufi influence), one common practice is to visit or make pilgrimages to the tombs of saints, renowned scholars, and righteous people. This is a particularly