I learned seventy surahs directly from the mouth of the Messenger of Allah ﷺ while Zayd bin Thabit was still a young boy with a forelock, attending the school.
حدثنا وكيع حدثنا سفيان عن أبي إسحاق عن خمير بن مالك قال
قرأت من في رسول الله ﷺ سبعين سورة وزيد بن ثابت له ذؤابة في الكتاب
Its isnad is sahih. Hujayr bin Malik Hamdani is trustworthy, Ibn Hibban deemed him trustworthy, and Bukhari mentioned him in al-Kabir 2/1/203, 207, and in this second location he narrated this hadith with the same meaning through his chain from Abu Ishaq Sabi. See also 3599, and see Fath al-Bari 9:43-44.