Shah Waliullah Dehlawi — in full Qutb al-Din Ahmad ibn 'Abd al-Rahim al-'Umari al-Dihlawi — was born on 21 February 1703 in Phulat, near Muzaffarnagar, and was raised in Delhi, where his father, Shah Abdur Rahim, had founded the Madrasah-i Rahimiyah. He is said to have memorised the Qur'an by the age of seven and to have completed the standard curriculum of his day by fifteen, succeeding his father as head of the madrasa two years later. In 1730–31 he made the hajj, then spent roughly a year in Medina studying hadith — chiefly under Abu Tahir al-Kurdi (also rendered al-Kurani), with further study under Muhammad Wafdullah al-Maliki and Shaykh Taj al-Din al-Qal'i — before returning to Delhi on 16 December 1732. He died there on 20 August 1762 (29 Muharram 1176 AH) and was buried beside his father. His other works include Hujjat Allah al-Baligha, generally reckoned his most important book, Al-Fawz al-Kabir, and Futuh al-Haramayn, his own account of the journey that took him to the Hejaz.
Al-Arba'in continues the same "forty hadith" (arba'iniyyat) tradition as [[NAW|al-Nawawi's Forty Hadith]] and [[QUD|Forty Hadith Qudsi]], tracing back to a hadith that promises a place among the scholars on the Day of Judgment to whoever preserves forty hadith concerning the religion — a hadith most critics themselves classify as da'if (weak) — and to a first, now-lost collection credited to Abdullah ibn al-Mubarak (d. 797). It differs from those two in what it gathers: rather than hadith selected by theme or canonical rank from across the wider literature, its English publisher describes it as forty hadith Shah Waliullah said he heard directly from his own teacher in Medina, each kept together with the chain of transmission (sanad) by which he received it — a personal record of transmission from the year of study that, by his son's account, changed how he taught and wrote once he returned to Delhi.
The Arabic text here is the classical matn, in the public domain. Beneath it in the reader sits an English translation, drawn from the fawazahmed0/hadith-api's eng-dehlawi edition and aligned hadith-for-hadith with the Arabic so the two can be read as a pair — the same companion arrangement this corpus uses for [[BUK|Sahih al-Bukhari]], [[MUS|Sahih Muslim]], [[ABD|Sunan Abi Dawud]], [[TIR|Jami` at-Tirmidhi]], [[NAS|Sunan an-Nasa'i]], [[IBM|Sunan Ibn Majah]], [[MAL|Muwatta Malik]], [[NAW|Forty Hadith of an-Nawawi]], [[QUD|Forty Hadith Qudsi]], and its Qur'an translations. Which published English translation this file itself descends from has not been pinned down on this corpus's side, which is why its licence is marked under review rather than public domain outright; the Arabic above it carries no such uncertainty.