Intro
Ahmadis are running around social media trying to convince the world that there is a universal definition of a Muslim.  They are wrong.  There is no universal definition.  In reality, it is up to ANY govt. to chose whether to define a Muslims or not.  I live in the USA, my govt. doesn’t collect stats on religion, nor are there any religious tests.  However, we do collect info on ethnicity and separate people on that basis.  Most Ahmadis don’t see this difference, they are confused, most likely since they have never actually used their own brains, they rely on the vicious Ahmadi mullahs for information.

A hadith on the topic
“Whoever says, ‘None has the right to be worshipped but Allah’, faces our Qibla (Mecca) during the prayers, prays like us and eats our slaughtered animal, then he is a Muslim, and has got the same rights and obligations as other Muslims have.” (Bukhari)

Commentary on this hadith?
MGA was silent on this hadith, Noorudin was silent on this hadith, Mirza Mahmood Ahmad was silent on this hadith.  Ahmadiyya leadership has never properly commentated on this hadith.

Questions about this hadith?
What is the context?  What year was it revealed?  If Shafi-Muslims pray with their hands differently then Hanafi-Muslims..then what?  What about Muhammad (Saw)??  Why isn’t he mentioned here?  Why does this hadith seem to indicate that belief in Muhammad (saw) and all prophets isn’t required?  And is Muhammad (Saw) talking in terms of Zakat only?  Or the difference in paying Zakaat and Jizya?  What if a Muslim doesnt pray 5 times per day???  Like some shias groups?  Then what?

What does the Quran tell us? 
4:136—140.  See Tafsir Ibn Kathir
http://www.qtafsir.com/index.php?option=com_content&task=view&id=595&Itemid=59

(136. O you who believe! Believe in Allah, and His Messenger, and the Book (the Qur’an) which He has sent down to His Messenger, and the Scripture which He sent down to those before; and whosoever disbelieves in Allah, His Angels, His Books, His Messengers, and the Last Day, then indeed he has strayed far away.)137. Verily, those who believe, then disbelieve, then believe (again), and (again) disbelieve, and go on increasing in disbelief; Allah will not forgive them, nor guide them on the (right) way.) (138. Give to the hypocrites the tidings that there is for them a painful torment.) (139. Those who take disbelievers for friends instead of believers, do they seek honor with them Verily, then to Allah belongs all honor). (140. And it has already been revealed to you in the Book that when you hear the verses of Allah being denied and mocked at, then sit not with them, until they engage in talk other than that; certainly in that case you would be like them. Surely, Allah will collect the hypocrites and disbelievers all together in Hell.)

Conclusions
This hadith is inconclusive…either that, or this was during the 5th year (ah) and Muhammad (Saw) hadn’t totally explained Islam yet and was giving out a lax definition.  Maybe…..this hadith was given out during a war?  Maybe this hadith was uttered during peace time.  We will never know.  However, the quranic verse is clear…a Muslim is one who accepts ALL the prophets of Allah.  Since Ahmadis consider Mirza Ghulam Ahmad a new prophet, they are either lying to the masses or deliberately playing-dumb, most likely they are a combination of the two.

In conclusion, there is no universal definition of a Muslim.  And this is exactly what the Govt. of Pakistan realized in 1953 when Mirza Mahmud Ahmad was made to come to court and be questioned.  Similarly, there is no universal definition of a Christian or a Jew or a Hindu.  So, obviously, Ahmadiyya leadership is playing a game with the public.