It is narrated from Imam al-Zuhri (may Allah have mercy on him) that the Messenger of Allah (peace and blessings be upon him) said: "None of you should ever bathe unless there is a person near him who does not look at him, staying close to him and talking to him."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 962