What are the times when it is forbidden to engage in ذكر (remembrance of God) and دعاء (supplication)?

Allah Almighty praised His servants who remember Him in every state. The Prophet, peace and blessings be upon him, used to remember Allah at all times. Scholars disliked remembrance with the tongue in impure places, out of reverence for the sanctity of Allah, but remembrance with the heart is permissible at all times and in all circumstances.