Musnad Ahmad 30:2439

Yahya ibn Sa'id narrated to us, from Fudayl ibn Ghazwan, who said: Ibn Abi Nu'm narrated to us, who said: Abu Hurayrah narrated to me, who said: Abu al-Qasim, the Prophet of Repentance, may Allah bless him and grant him peace, narrated to us, saying: "Whoever accuses his slave of something of which he is innocent, he will have the prescribed punishment (hadd) established against him on the Day of Resurrection, unless he is as he said."