I believe he traced it back to the Prophet ﷺ, who said, "Whoever lies about a dream he claims to have seen will be charged on the Day of Resurrection with tying a knot in a barley grain."
حدثنا عبد الله حدثني إسحاق بن إسماعيل حدثنا قبيصة حدثنا سفيان عن عبد الأعلى عن أبي عبد الرحمن
أراه رفعه قال من كذب في حلمه كلف عقد شعيرة يوم القيامة
Its isnad is daif, because of Abdul-Ala as well. Qabisa is Ibn Uqba bin Muhammad Sawai, and he is trustworthy and reliable, and whoever criticized his narration from Thawri has no basis for it. The hadith is a repeat of 1070, and see 1075.