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(Arabic: "keeping vigil"), in Islamic practice, the recitation of the Qur'an (Islamic scriptures) and prayers during the night. Tahajjud is generally regarded as sunnah (tradition) and not fard (obligation). There are many verses in the Qur'an that encourage these nightly recitations and other verses that indicate such practices should remain "a voluntary effort" (17:79). Pious Muslims everywhere perform tahajjud as a form of asceticism in imitation of the Prophet Muhammad, who continued nightly vigils even after the institution of the five daily prayers. In fiqh (Islamic jurisprudence), it is considered blameworthy to prevent those who desire to do so from practicing tahajjud as much as they wish. According to one tradition, tahajjud "loosens the knots that Satan ties in the hair of a sleeper." During Ramadan (the Muslim month of fasting) tahajjud is considered particularly meritorious, so Muslims often spend these nights in mosques praying and reciting the Qur'an until dawn. In some Muslim countries an official nighttime adhan (call for prayer) has been instituted.