Conditions:
1. Continuous chain (muttasil)
2. All narrators are trustworthy ('adil)
3. All narrators have strong memory (dabit)
4. Free from shudhudh (irregularity)
5. Free from 'illa (hidden defect)
Examples: Sahih al-Bukhari, Sahih Muslim
Meets Sahih conditions but narrator has slightly weaker (though acceptable) memory. Acceptable as evidence.
Fails one or more Sahih conditions. Causes of weakness:
Fabricated hadith are not merely weak — they are lies attributed to the Prophet ﷺ and are haram to spread.