Read all Ahadith in chapters on witnesses by jami al tirmizi

Zaid bin Khalid Al-Juhani narrated that the Messenger of Allah (s.a.w) said: Shall l not inform you of the best of witnesses? The one who comes with his testimony before being asked for it.

(Another chain) from Malik in which he said: Ibn Abi 'Amrah.

Zaid bin Khalid Al-Juhani narrated that the Messenger of Allah(s.a.w) said: The best of witnesses is the one who gives his testimony before being asked for it.

Aishah narrated that the Messenger of Allah (s.a.w) said: The testimony of a treacherous man is not acceptable nor a treacherous woman nor a man lashed for the Hadd nor a woman lashed nor one possessing malice of enmity nor a rehearsed witness nor the Qani of (one contracted by)the family on their behalf nor the one associating himself to other than his Wala or to other than his relatives.

Ayman bin Khuraim narrated that the Prophet (s.a.w) stood to give a Khutbah and said: O you people False witness is tantamount to Shirk with Allah Then the Messenger of Allah (s.a.w)recited: So shun the Rijs of the idols, and shun false speech.

Khuraim bin Fatik Al-Asadi narrated that the Messenger of Allah (s.a.w) performed the Subh (Fajr)prayer. Then when he turned he got up to stand and said: O you people! False witness is tantamount to Shirk with Allah. Saying it three times, then he recited this Ayah And shun false speech Until the end of the Ayah.

Abdur-Rahman bin Abi Bakrah narrated from his father that the Messenger of Allah (s.a.w) said: Shall I not inform you of the greatest of the major sins? They said: Of course O Messenger of Allah(s.a.w)! He said: Shirk with Allah disobeying parents, and false testimony. Or: False speech He said: So the Messenger of Allah(s.a.w) would not stop saying it until we said ( to ourselves): 'I wish he would be quiet.

Imran bin Husain narrated that the Messenger of Allah(s.a.w)said: The best of people are my generation, then those who follow them,then those who follow them, then those who follow them. (He(s.a.w)said that) three times. Then, after them a people will come who increase in fatness, loving fatness, giving testimony before they are asked for it.

Clarification of this is in the Hadith of 'Umar bin Al-Khattab, from the Prophet(s.a.w) who said: The best of people are my generation, then those who follow them,then those who follow them. Then lying will spread, until a man testifies while his testimony was not requested, and a man will take an oath while an oath was not sought.