Hadeeth means the words, actions, approvals or attributes that have been narrated from the Messenger (peace and blessings of Allah be upon him).
A hadeeth may either confirm things that are mentioned in the Quran, such as prayer, zakah (poor-due), etc., or it may give details of things that are mentioned in the Quran in general terms, such as the numbers of rak’ahs (units) in each prayer, the thresholds for paying zakah, the details of Hajj, etc. It may also explain rulings which are not mentioned in the Quran, such as the prohibition on being married to a woman and her (paternal or maternal) aunt at the same time.
Allah revealed the Quran to His Messenger Muhammad (peace and blessings of Allah be upon him) and commanded him to explain it to the people, as He said (interpretation of the meaning):
“And We have also sent down unto you (O Muhammad) the Dhikr [reminder and the advice (i.e. the Quran)], that you may explain clearly to men what is sent down to them, and that they may give thought.”
The hadeeth of the Messenger (peace and blessings of Allah be upon him) is a revelation (wahy) from his Lord. Allah says (interpretation of the meaning):
“Your companion (Muhammad) has neither gone astray nor has erred.
Nor does he speak of (his own) desire.
It is only a Revelation revealed.”