the Fatwa Department Research Committee - chaired by Sheikh `Abd al-Wahhâb al-Turayrî
It is neither prohibited nor even disliked for a Muslim to speak while standing in the bathroom. What is regarded as disliked is for a Muslim to speak while relieving himself, whether he is in a room dedicated for that purpose or out in the wilderness.
The desirability of remaining quiet does not apply to the bathroom as a room, but to the action of relieving oneself.
It is disliked in Islam – but merely as a matter of bad form – to speak unnecessarily while relieving ourselves. It is not prohibited.
Please know that it is not disliked in a case where there is a reason to speak. For example, one clear case of necessity would be to ask for water to clean yourself if sufficient water is not present.
The following hadîth, moreover, is weak:
Abû Sa`îd said: I heard the Prophet (peace be upon him) saying : “Two men should not go to relieve themselves, exposing their private parts, and then be talking to each other, since Allah hates that.” [Sunan Abî Dâwûd (15) Sunan Ibn Mâjah (342) and Musnad Ahmad (10884)]
And Allah knows best.
Source: Islam Today