روي عن الإمام أحمد رحمه الله أنه قال: صح من الحديث سبعمائة ألف وكسر، وحمله أهل العلم على ما يشمل الأحاديث النبوية وأقوال الصحابة والتابعين.
It is narrated that Imam Ahmad (rah) said: “What is the Sahih from al-Hadith are 700,000 and a little more, the scholars of Islam considered that amongst them are prophetic Hadiths and the sayings of the Sahaba and Tabi’een and Imams in the same Matn but with different chains.”
وذكر الإمام البخاري رحمه الله أنه يحفظ مائة ألف حديث صحيحة، وحمله أهل العلم على اختلاف الأسانيد مع تكرار المتون.
Imam al-Bukhari (rah) mentioned that he memorised 100,000 Sahih Hadith, the scholars of Islam considered that he meant Hadiths of similar Mutoun but different Asanid.
وذكر الإمام النووي رحمه الله أن الأحاديث الصحيحة (أي المحتج بها فتشمل الحسنة) قريب من عشرة آلاف حديث.
Imam al-Nawawi (rah) mentioned that the Sahih hadiths (meaning those which can be used as hujjah so it includes Hasan) are near 10,000.
And this number is close to the number of Hadith in sheikh al-Albani’s book Sahih al-Jami’i (more than 8,000).
As for the biggest Musnad we have today it is Musnad Ahmad which has around 40,000 amongst them are 10,000 with repeated Isnads, thus it seems Ahmad collected his Musnad from the 700,000.
جمعت كتاب السنن من ستمائة الف حديث.
Abu Dawoud (rah) said: I collected the narrations in my book of Sunan from 600,000.
meaning he had 600,000 Hadiths, different chains for the exact same Hadith in which one Hadith could have around 20 to 30 chains, also it’s not all prophetic Hadiths.
The first scholars used to call the Tariq and the Sanad a Hadith, so if Bukhari said ” I memorised 20 hadiths” he could mean that he memorised 20 ways for the same Hadith.
Egyptian Sheikh of Hadith Abu Ishaq al-Huweini said about the number of Sahih hadith after Hussein Ya’aqoub asked him: “they do not reach 20,000.”
what he probably means are those who are Sahih in Sanad (Around 4,400) and you add to them those who are Hasan li-Thatihi and al-Hadith al-Hasan li-Ghayrihi then you might get this amount or a little less.
Also do not forget that the number of Sahih Hadith outside Bukhari and Muslim is very big and I doubt anyone has gathered and authenticated all of it, even al-Albani skipped a lot of Hadiths which he did not deem Sahih or Da’eef and he changed his opinions about others later.
Just recently one of the respectable scholars of kurdistan made an encyclopaedia called “Sahih wa Da’eef tareekh al-Tabari” and many more scholars are working on authenticating the entire Sunnah if possible, so we cannot say with Jazm what is the number of Sahih Hadith in Islam.