BOTH DHIKR AND talking are makrūh whilst relieving oneself, whether outdoors or in a building. This applies to dhikr and speech except what is necessary, so much so that some of our colleagues state that even if a person sneezes he should not praise Allah 
, nor should he respond to one who sneezes, return a greeting, or respond to the mu’adhdhin. Anyone who greets him will be neglectful [of this ruling] and will not deserve a reply. All such talk is makrūh in order to be free of imperfection but it is not ḥarām. If one sneezes and praises Allah in his heart without moving the tongue there is no harm; one should do likewise during sexual intercourse.
, nor should he respond to one who sneezes, return a greeting, or respond to the mu’adhdhin. Anyone who greets him will be neglectful [of this ruling] and will not deserve a reply. All such talk is makrūh in order to be free of imperfection but it is not ḥarām. If one sneezes and praises Allah in his heart without moving the tongue there is no harm; one should do likewise during sexual intercourse.And we relate from Ibn ‘Umar 
that a man passed by the Messenger of Allah 
while he was urinating and greeted him, but he did not reply. Muslim narrated it in his Ṣaḥīḥ. [1].
that a man passed by the Messenger of Allah while he was urinating and greeted him, but he did not reply. Muslim narrated it in his Ṣaḥīḥ. [1].Al-Muhājir ibn Qunfudh 
said: “I came to the Prophet while he was urinating and I greeted him. He did not reply until he had performed ablution. Then he apologised to me and said: ‘I dislike making mention of Allah when I am not in a state of purity (ṭuhr)’– or else he said, ‘ritual purity (ṭahārah)’.’” [2].This hadith is ṣaḥīḥ. Abū Dāwūd narrated it, as did an-Nasā’ī and Ibn Mājah with ṣaḥīḥ isnāds.
said: “I came to the Prophet while he was urinating and I greeted him. He did not reply until he had performed ablution. Then he apologised to me and said: ‘I dislike making mention of Allah when I am not in a state of purity (ṭuhr)’– or else he said, ‘ritual purity (ṭahārah)’.’” [2].This hadith is ṣaḥīḥ. Abū Dāwūd narrated it, as did an-Nasā’ī and Ibn Mājah with ṣaḥīḥ isnāds.References
[1] Muslim (370) and an-Nasā’ī (1/36).
[2] Abū Dāwūd (17), an-Nasā’ī (1/37), and Ibn Mājah (350).