Why does Nawawi's Forty Hadith contain 42 ahadith?

Question

"An-Nawawi's Forty Hadith" has always been my favorite book of ahadith; it was the first one I ever bought and remains highly recommended reading for anyone interested in the fundamentals of Islam.

However, one thing about this compilation has always bothered me; despite being entitled "Forty Hadith", my copy obviously contains 42 ahadith.

I had originally thought this may just be a quirk of translation (my copy is translated by Ezzeddin Ibrahim and Denys Johnson-Davies), but I have seen the same 42-hadith breakdown used in Sunnah.com's collection; not sure which translator they used, but the translation is clearly different from my own copy.

Having never read the original Arabic compilation, I can't be certain that this isn't yet a translation quirk, but two separate translations with the same clearly-defined numbering scheme casts doubt on that theory.

Presumably, in addition to being one of the most celebrated scholars in Shafi'i jurisprudence, Imam An-nawawi was at least basically competent in counting. Which leaves me scratching my head over the question, why does his famous Forty Hadith have two too many ahadith?

This might seem a silly question, but it's really been driving me nuts for a while.

Answer 1

Note: In the following, I'll be translating from Arabic language as these translations are mainly my own take them with the necessary care!

Sheikh ibn 'Otaymeen said explaining this issue:
"The forty hadith of an-Nawawi and strictly speaking they are not forty, but forty-two, but the Arabs used to round fractions in numbers, so they say: forty even if it was more by one or two or less by one or two.

These forty should be memorized by any student of knowledge because they are chosen out of many ahadith out of many different topics. In difference to most other books for example, if we take 'Omdat al-Ahkam which indeed is a good selection, but it only covers one single topic: fiqh. The forty of hadith of an-Nawawi cover different topics, and we ask Allah for help and guidance to comment on them. And Allah is the Compromising"

و بين فضيلة الشيخ محمد بن صالح العثيمين الأربعون النووية، وهي ليست أربعين،بل هي اثنان وأربعون، لكن العرب يحذفون الكسر في الأعداد فيقولون: أربعون. وإن زاد واحداً أو اثنين، أونقص واحداً أواثنين.

هذه الأربعون ينبغي لطالب العلم أن يحفظها،لأنها منتخبة من أحاديث عديدة. وفي أبواب متفرقة،بخلاف غيرها من المؤلفات فلو نظرنا إلى عمدة الأحكام لوجدناها منتخبة؛ لكنها في باب واحد وهو باب الفقه، أما الأربعون النووية فهي في أبواب متفرقة متنوعة. ونحن نستعين بالله تعالى في التعليق عليها. والله الموفّق. .(source)

So we may conclude that "the forty" is based on the understanding of Arabs of what the amount "forty" may refer to in the colloquial language or the use of language.

In his commentary on the 40 ahadith ibn Daqiq al-'Id commented the weak hadith about forty ahadith in imam an-Nawawi's introduction, explaining that 40 is the first number which has a "full number" (natural number) as the result of the fraction (for Zakat on capital assets) of the quarter of the tenth (1/40) and from the hadith -he didn't mention which exactly- one can conclude that the quarter of the tenth cleans the rest of the wealth. And this applies for those whom apply any (one) of these ahadith in their lifes.
Ibn Daqiq al-'Id didn't comment on the fact that the collection includes 42 instead of 40 ahadith, as if this was something unimportant, which seems to emphasize the statement from above, that it was "business as usual" or "usual practice" to speak about 40 ahadith while they were 42.

Answer 2

Abu 'Amr ibn as-Salah first compiled 26 ahadith that he considered to encompass the major components of Islam and that he considered to be from the concise and meaningful sayings (jawami'ul kalim) of the Prophet (saws). He started teaching these ahadith, and when Imam an-Nawawi came after him, he felt there should be more included. He added more ahadith until they became 42, and he named it Nawawi's Forty (Al-Arba'in an-Nawawi). He mentions in the introduction a (weak) hadith about the virtues of collecting 40 hadith but also says that he relies upon stronger traditions as the basis of his work. It has always been 42 hadith, it's just called his "forty."

Ibn Rajab al-Hanbali came along later, added 8 ahadith, made it a round 50, and explained them all in his tome "Al-Jami' al-Ulum wa al-Hikam."