The Messenger of Allah ﷺ said, "Shall I not tell you about the best of witnesses? They are those who come forward with their testimony before being asked for it."
حدثنا صفوان بن عيسى قال أخبرنا محمد بن عمارة عن أبي بكر بن محمد عن عبد الله بن عمرو
أن رسول الله ﷺ قال ألا أخبركم بخير الشهادة الذين يبدءون بشهادتهم من غير أن يسألوا عنها
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Its isnad is sahih. It has already appeared at 16977. Muhammad bin Umara was deemed reliable by the scholars, though he has some errors, and his hadith was only confirmed sahih because of the corroborating narration that will come later. Abu Bakr bin Muhammad is Ibn Amr bin Hazm, a well-known reliable narrator praised by the leading scholars, and likewise his cousin Abdullah bin Amr bin Uthman bin Affan al-Umawi.