Musannaf Ibn Abi Shayba 13:906

Abu Bakr narrated to us, he said: Muhammad ibn Mus'ab narrated to us, from al-Awza'i, he said: I asked Qatadah about the "secluded gift" (al-'atiyyah al-khalwah). He said: "That is showing off (sum'ah); it is not permissible."