Sahih, hasan and da'if

Scholars graded hadith by the strength of the chain and the soundness of the text:

• Sahih (sound): an unbroken chain of upright narrators with precise memory, free of hidden defects.
• Hasan (good): like sahih, but with a narrator whose precision is a little less.
• Da'if (weak): a report that falls short of those conditions, for example through a break in the chain or a weak narrator.

A report known to be fabricated is not a hadith of the Prophet at all and may not be passed on as one.

In the Forty Hadith you will see Imam an-Nawawi state the source and often the grade himself, for example "related by al-Bukhari and Muslim" or "a hasan hadith related by at-Tirmidhi". On this site those words are shown exactly as he wrote them.