Musannaf Ibn Abi Shayba 26:292

Muhammad ibn Bishr narrated to us, he said: Sa'id narrated to us, from Qatadah, from Ali and Zayd regarding the son of the *mula'anah* (the woman involved in the imprecation process): They both said: "One-third is for his mother, and what remains is in the public treasury (*bayt al-mal*)."