al-Arba'un al-Nawawiyya (Nawawi's Forty)

Al-Nawawi gathered in this book comprehensive hadiths that he took from the session of "Al-Ahadith al-Kulliyya" by Ibn al-Salah, which had twenty-six hadiths. He then added to them until they reached forty-two, and called his book "Al-Arba'un" (The Forty). The book became well known and was widely memorised, and commentators wrote a great deal on it. ¹