Explanation

6 books of Ahadis also known as sihah e sitta 

Sahih Bukhari, collected by Imam Bukhari 

Sahih Muslim, collected by Muslim 

Sunan al-Sughra, collected by al-Nasa'i 

Sunan Abu Dawood, collected by Abu Dawood 

Jami al-Tirmidhi, collected by al-Tirmidhi 

Sunan ibn Majah, collected by Ibn Majah