Jami` at-Tirmidhi 2297
جامع الترمذي#2297SahihZaid 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
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Ahmad Muhammad ShakirSahih Lighairihi
Zubair Ali ZaiSahih
In-book reference: 35:3