Ahmad bin Hanbal said: "What Isma'il bin Ayyash narrates from the people of Syria is sahih (authentic), and what he narrates from the people of the Hijaz is not sahih."
Al-Shaykh (al-Bayhaqi) said: Al-Bukhari and a group of the hadith masters said the same, and this hadith Isma'il narrated only from a Syrian; and Allah knows best. It has also been narrated through another route from the hadith of the people of Syria.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الوصايا / 12538