Based on the account in the Gospel of John, chapter 8, Jesus is described as writing on the ground (often interpreted as sand or dust) two times.
This occurs during the story where the scribes and Pharisees bring a woman caught in adultery to Jesus, testing him regarding the Law of Moses which commanded such women be stoned.
First instance (John 8:6): After the accusers present the woman, "Jesus bent down and wrote with his finger on the ground."
Second instance (John 8:8): After challenging the accusers by saying, "Let him who is without sin among you be the first to throw a stone at her," the text states, "And once more he bent down and wrote on the ground."