Al-Sahifat Al-Sajjadiyya is the oldest prayer manual in Islamic sources and one of the most seminal works of Islamic spirituality of the early period. It was composed by the Prophet's great grandson, `Ali ibn al-Husayn(as), known as Zayn al-'Abidin (`the adornment of the worshippers'), and has been cherished in Shi'ite sources from earliest times. Zayn al-'Abidin (as)was the fourth of the Shi'ite Imams, after his father Husayn(as), his uncle Hasan(as), and his grandfather 'Ali(as), the Prophet's son-in-law. Shi'ite tradition considers the Sahifa a book worthy of the utmost veneration, ranking it behind only the Qur'an and `Ali's Nahj al-balagha.The Sahīfa al-Sajjādiyya is an epic in Muslim devotional literature and liturgy. Its contents are both theological and ethically edifying in nature.