Musnad Ahmad 26:640

'Abd al-Rahman ibn Mahdi narrated to us, Sufyan narrated to us, from Mansur and al-A'mash, from Abu Wa'il, from 'Abdullah, from the Prophet (peace and blessings of Allah be upon him), who said: "If you are three, then two of you must not whisper privately to the exclusion of the third. And a woman must not touch another woman and then describe her to her husband, as if he were looking at her." He (the narrator) said: I think Mansur said: "Unless there is a garment between them."