Sahih Muslim
The Book Pertaining to Judicial Decisions (Kitab Al-Aqdiyya)
Book Number: 018 / Hadith Number: 4268
Zaid b. Khalid al-Juhani reported Allah's Apostle (may peace be upon him) as saying: Should I not tell you of the best witnesses? He is the one who produces his evidence before he is asked for it.