Imam al-Bukhari (may Allah have mercy on him) says that Yahya bin Sa'id al-Qattan said: Sayf bin Sulayman was alive in the year (1)50, and in our view he was a thiqah (trustworthy) narrator, truthful and one who retained well (hafiz).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 20641