It is narrated from Hazrat Zaid bin Khalid (may Allah be pleased with him) that the Noble Prophet (peace and blessings be upon him) said: Shall I not tell you about the best of witnesses? The one who is ready to give testimony (of the truth) before being asked to do so.
Hadith Referenceمسند احمد / مسند الأنصار رضي الله عنهم / 21687
Hadith Gradingحکم دارالسلام:حديث صحيح، وهذا إسناد ضعيف لضعف أبى بن عباس، وقد وهم، وقد خولف