Al-Awza'i (may Allah have mercy on him) said: I kept concealing it, but then I saw that it had spread, meaning the hadith of Ibn Busr (may Allah be pleased with him) concerning fasting on Saturday.
(The hadith of Juwayriyah bint al-Harith (may Allah be pleased with her) has already passed in the previous chapter, which indicates that fasting on Saturday is permissible; it is as though what is meant by the prohibition is fasting on that day out of veneration for it.)
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8496