Ibn Muayiz Saadi reported,

I went out at dawn to water a horse of mine and passed by the mosque of Banu Hanifa, where I heard them saying that Musaylima was the messenger of Allah. So I went to Abdullah and informed him. He sent the guards, who brought them in, and he called on them to repent. They repented, so he set them free, but he had Abdullah bin an-Nawwaha beheaded.People said to him, "You took a group of men for a single offense, then killed some of them and let the others go?"He replied, "I heard the Messenger of Allah ﷺ when this man and Ibn Uthal bin Hujr came before him. He asked them, 'Do you two bear witness that I am the Messenger of Allah?' They answered, 'We bear witness that Musaylima is the messenger of Allah.' The Prophet ﷺ then said, 'I believe in Allah and His messengers. Were I one to kill envoys, I would have killed you both.' That is why I had him executed."

Ahmad 3837

Sahih

حدثنا سليمان بن داود الهاشمي أنبأنا أبو بكر بن عياش حدثنا عاصم عن أبي وائل

عن ابن معيز السعدي قال

خرجت أسقي فرسا لي في السحر فمررت بمسجد بني حنيفة وهم يقولون إن مسيلمة رسول الله فأتيت عبد الله فأخبرته فبعث الشرطة فجاءوا بهم فاستتابهم فتابوا فخلى سبيلهم وضرب عنق عبد الله بن النواحة فقالوا آخذت قوما في أمر واحد فقتلت بعضهم وتركت بعضهم قال إني سمعت رسول الله ﷺ وقدم عليه هذا وابن أثال بن حجر فقال أتشهدان أني رسول الله فقالا نشهد أن مسيلمة رسول الله فقال النبي ﷺ آمنت بالله ورسله لو كنت قاتلا وفدا لقتلتكما فلذلك قتلته

أحمد 3837صحيح
Contents
Reference
Commentary
Ayat
Collection
Musnad Ahmad
Book
Abdullah bin Masud
Numbering
Darussalam 3837
Ahmad 3837