קבלה אויף ירמיהו 1:5

When the patriarch Abraham comprehended the great truism, revolved it in his mind, conceived it perfectly, made careful investigations and profound inquiries, pondered upon it and succeeded in contemplations, the Lord of the Universe appeared to him, called him his friend, made with him a covenant between the ten fingers of his hands, which is the covenant of the tongue, and the covenant between the ten toes of his feet, which is the covenant of circumcision, and said of him : "Before I formed thee in the belly I knew thee." (Jer. I, 5.)