Full title: Al-Jami' al-Musnad al-Sahih al-Mukhtasar
Author: Muhammad ibn Ismail al-Bukhari (810–870 CE)
Hadiths: ~7,563 (with repetitions); ~2,602 unique
Al-Bukhari selected from 600,000 hadiths he memorised. He spent 16 years compiling it, performing ghusl and 2 rak'at before recording each hadith. Scholars say it is the most authentic book after the Quran.
Full title: Al-Musnad al-Sahih al-Mukhtasar
Author: Muslim ibn al-Hajjaj al-Nisapuri (815–875 CE)
Hadiths: ~7,470 (with repetitions); ~3,033 unique
Imam Muslim was a student of Imam Bukhari. His method: he grouped all chains for each hadith together, making it easier to study variations. He selected from 300,000 hadiths.