He used to begin his narration by saying, "The Messenger of Allah ﷺ, Abu Qasim, the truthful and trusted, said, 'Whoever lies about me deliberately, let him take his seat in the Fire.'"
حدثنا عفان قال حدثنا عبد الواحد يعني ابن زياد قال حدثنا عاصم بن كليب قال حدثني أبي قال سمعت
يقول وكان يبتدئ حديثه بأن يقول قال رسول الله ﷺ أبو القاسم الصادق المصدوق من كذب علي متعمدا فليتبوأ مقعده من النار
Its isnad is sahih, it passed at 3265, and the hadith is found in all the major collections, Bukhari 1/38, in the Book of Knowledge, on the sin of lying about the Prophet ﷺ, Muslim 1/30 no. 3, in the introduction, Abu Dawud 3/320 no. 3651, in the Book of Knowledge, on the severity of lying about the Messenger of Allah ﷺ, and Tirmidhi 4/524 no. 2257, in the Book of Tribulations, and he said, hasan sahih.