Bulugh al-Maram 1414
Narrated Zaid bin Khaled al-Juhani (RA):
The Prophet (ﷺ) said: "Shall I not inform you who is the best witness? He is the one who produces his testimony before he is asked for it."

[Reported by Muslim].
عَنْ زَيْدِ بْنِ خَالِدٍ اَلْجُهَنِيِّ ‏- رضى الله عنه ‏- أَنَّ اَلنَّبِيَّ ‏- صلى الله عليه وسلم ‏-قَالَ: { 
"أَلَا أُخْبِرُكُمْ بِخَيْرِ اَلشُّهَدَاءِ? اَلَّذِي يَأْتِي بِشَهَادَتِهِ قَبْلَ أَنْ يُسْأَلَهَا" }  رَوَاهُ مُسْلِم ٌ  1‏ .‏‏1 ‏- صحيح.‏ رواه مسلم ( 1719 )‏.‏