ANSWER:

You cannot call anyone kafir. To judge people is not our responsibility. Only scholars can label him as such after fulfilling the conditions and ensuring there are no obstacles between him and kufr! He could be praying when people don’t see him. 

i know someone who doesn’t pray at all. not even juma’a. but in ramadan he fast but still in ramadan he doesn’t pray. that means he fasts without praying at all. does it mean that he is a kafir? and shall i consider him and call him a kafir?