Meaning all narrators have strong memory.

Warning: Later scholars, recognizing differences in memory strength, coined the term “Hasan” for narrations from narrators with less than perfect precision, whereas earlier scholars did not differentiate and considered every precise narration as “Sahih.” Some early scholars used “Hasan” differently. There is a misconception that early scholars did not consider Hasan Hadith authoritative, but this is not true; they simply did not use the term “Hasan,” and used “Sahih” instead.