Musannaf Ibn Abi Shayba 19:642

Abu Bakr narrated to us, he said: Hafs and 'Abbad bin al-'Awwam narrated to us, from Hajjaj, from al-Zuhri, who said: The Sunnah of the Messenger of Allah (may Allah bless him and grant him peace) and the two Caliphs after him has passed that the testimony of women is not permissible in the prescribed punishments (hudud).