Musnad Ahmad 5:524

Abdullah narrated to us, Ishaq bin Ismail narrated to us, Qabisah narrated to us, Sufyan narrated to us, from Abd al-A’la, from Abu Abd al-Rahman, from Ali, who said—I think he attributed it to the Prophet (ﷺ)—he said: "Whoever lies about a dream he has seen shall be tasked with tying a knot in a barley grain on the Day of Resurrection."