Is it bad to ask a fellow Muslim brother who is my friend, if he prayed Salah or not?

Yes. It is very wrong to ask people if they have prayed.

It is none of your business. It is only between them and allah.

If they have prayed everything is fine, if they have not, their social status decreases. Naturally everybody prays, it is as if you asked people if they wiped their ***. Incredibly impolite. You can not even expect an honest answer, because people who did not pray, would never admit.

Salam No it.is not bad if you ask your fellow if he prayed salah or not.It is good for reminding him so it is recommended

It is wrong, because you should always have the best opinion of other Muslims, and not be suspicious and not spy and not try to cause them to reveal their good deeds, so on..... All this is basic etiquette.

Assalamualaikum,

If by showing off he means that you are enjoining good/forbidding evil to show off then he is wrong. This is an obligation. A better way to word your question would be "If you didn't pray salat then you should go pray because it is time to pray." That way he doesn't have to reveal any of his good deeds because concealing them is more rewarding.

Before enjoining good and forbidding evil, I have found that you have to soften their hearts first because mankind today has hard hearts. Everyone thinks they're right, once someone's made up their mind it is hard to change it, unless you do this. You compliment them first, if they are Muslim then ask Allah ta'ala to reward them for any good deed you know they did, like coming to the masjid. When I enjoin good and forbid evil at my masjid, the first thing I say is "Assalamualaikum dear brother, may Allah ta'ala reward you for coming to the masjid and praying. I just wanted to let you know that I read this (Quran/hadith/fatwa/tafsir/etc) that says ....(enjoin good/forbid evil here)."

Then they will respond kindly (most of the time based on my experience). With regards to a kafir you could compliment them being funny and intelligent. You should invite them to Islam in a way that honors them. What I say is: "It is not worthy of someone who is as intelligent as you are to continue rejecting Islam, you are way too intelligent for this, come let us discuss."

This works well, and you could use the second method in guiding Muslims to. "You (a Muslim) are unworthy of committing this sin, someone as intelligent as you is above this my dear brother/sister."

You see? Soften their hearts, then enjoin good and forbid evil. Early on in my dawah I did it like you and got yelled at a few times, not that it stopped me, but it was harder that way, this way is easier.

In situations where a person, a Muslim for example, is doing some sin publicly, or spreading false information, you inform them firstly kindly. If they reject your evidence based on the Ulemas interpretation, and continue spreading falsehood (hypocrisy) then you can be aggressive against them. One brother at the masjid was talking to this revert about j1had being abolished, I provided him multiple ahadith and Quran (how is fasting prescribed and j1had also prescribed in Quran, yet one is abolished? Lol) and he continued and even raised his voice at me, so I got louder and raised my voice at him and assured him that if he continued interpreting Islam based on whims and desires he would take his seat in the fire. It was amusing lol he was like "IT IS NOT PART OF ISLAM, WE DON'T NEED TO LISTEN TO SCHOLARS (referenced), and I said "I SWEAR TO ALLAH SUBHANA WA TA'ALA, I SWEAR ON HIM WHOSE HAND MY SOUL IS IN, ANY ONE WHO INTERPRETS ISLAM BASED ON WHIMS AND DESIRES WILL TAKE THEIR SEAT IN THE FIRE. I SWEAR TO ALLAH." (referenced) and he quieted down, later he said something about jizya that was false and I said "NO NO, IF MUSLIMS ARE IN POWER THEN THEY HAVE TO IMPLEMENT JIZYA, NO QUESTION." (referenced) You can't back down from these guys, the revert agreed with me and the older man submitted and I taught him about the jizya as well, idk if he accepted it or submitted in silence, in any case I was able to prevent this false information from spreading by the leave of Allah ta'ala, Alhamdullilah, it was a gift from Allah ta'ala to stop this innovation and to defend the sunnah which is more rewarding than fasting, j1had, etc which are all good deeds for yourself, but protecting the sunnah is for the people (based on what Imam Ahmad (r.a) said) huge unimaginable reward in it, to stop innovation, and to revive sunnahs. Shaytan loves innovation more than sin, because you can repent from sin, but not from innovation (people do it in ignorance).

wa salam.