The Sahih and the Hasan Hadith
Question :
What is a Sahih Hadith? What is a Hasan Hadith? And which one is binding, meaning, which one must we apply it?
Answer:
The difference between the two is that the Sahih Hadith is that which is narrated by a trustworthy and completely precise narrator, with a connected chain that is safe from being Shath (an oddity) and from any damaging deficiency.
The Hasan Hadith is that which is narrated by a trustworthy narrator, and he has the same, with the exception of the precision, which is not a condition for a Hasan Hadith. So we may define it by saying it is that which is reported by trustworthy narrators, who have nominal precision, with a connected chain, that is safe from any Shath (oddity) and from any damaging deficiency.
Both categories, the Sahih and the Hasan are used as a proof and are to be acted upon.
Source:
Ibn 'Uthaimeen
Fatawa Islamiyah, Vol. 7 Page 162