He attributed it to the Prophet ﷺ, "When the evening meal is served and the prayer is called, begin with the meal."
حدثنا سفيان عن هشام عن أبيه
تبلغ به النبي ﷺ إذا وضع العشاء وأقيمت الصلاة فابدءوا بالعشاء
Its chain of transmission is sahih. It is found in Bukhari 2/169 in the chapter on manners, Muslim 1/392 no. 557 in the chapter on mosques, Abu Dawud 3/345 no. 3757 in the chapter on foods, and Tirmidhi 2/186 no. 354 in the chapter on prayer, where he said, hasan sahih.