Ok, I've read many posts of Guru Nanak being Muslim that was written by Muslims and many posts by Sikhs being angry and rejecting those posts. Well, my last name is "Singh" so you clearly know what I am.
Anyway I'm actually having a different approach to this. First of all, just to give a little introduction, sikhism came into India during the 1500's and Khalsa came in around the 1600's established by Guru Gobind Singh. As far as Monotheism goes (belief of one God) it was brought in India by the Muslims who came from Persia, Middle East, and Afghanistan.
Guru Nanak indeed was born in a Hindu family as a Hindu but however started to reject many aspects of it (beliefs, rituals, etc). Being around and being friends with many Muslims, he started to act like them, he started to read the Quran as well because it really caught his attention since it was very different than his own religion (Hinduism).
Let's take a moment to analyse this, if one person is used to doing something one way and all of a sudden he is exposed to doing it another way then obviously he will be curious and inquire about it even if he/she doesn’t like it, it's human nature.
For example, if you aren’t not friends with someone any more, and you don’t see them for a long time, if you meet someone who knows them, you're obviously going to ask about them.
Anyway, in this case he liked what he read, he learned how to read and write in Arabic as well. Not only did he read the Quran, he had read the Hindu scriptures as well. He had always rejected Hindu beliefs and customs however he never rejected Islamic customs. He had even gone to Mecca and performed Hajj, he had even stopped by Baghdad, stayed for 2 weeks, and performed the Islamic prayers there as well.
To be on the safe side I'm not going to say he was Muslim, but the facts say that since the incident of him coming out of the water, he had been chanting "Na koi hindu na muselmaan" and he also started to carry the Quran where ever he went, he also started to wear the Jubba (dressed like a Sufi).
It was then when he was rejected by many Hindus including his family, no one understood him. We don't realize what times he had faced, he started out as a runaway with some food, then he started to run out of food and started eating less, then he ran out of food completely and started to take milk from a cow if he saw one, until it came to a point where he starved risking his life. He could have just simply gave in to his father and said "Ok, I accept everything" but he didn't.
Anyway after coming back from Mecca he wore a robe that had Islamic writings all over it which is still kept at a Gurdwara in India. One thing that I want everyone to know is, GURU NANAK WAS NOT THE FOUNDER OF SIKHISM, FOR GOD SAKE THE GURU GRANTH SAHIB WASN'T EVEN FORMED UNTIL THE 3RD GURU.
During the 1st and 2nd Guru's time, THERE WAS NO SUCH THING AS SIKHISM, THERE WAS ONLY HINDUISM AND ISLAM, THAT IS A FACT!!!! SO I ASK WHAT RELIGION WAS GURU NANAK THEN REALLY???, IT'S NOT A COINCIDENCE THAT HE WASN'T CREMATED NOR BURIED.
I know what he was but it's better if people research, travel seven sea's and FIND OUT for themselves just like I did. Since Guru Nanak was a mystic sufi, just all the other mystic sufi's at the time, he wrote down all of his ideas in poetic form (they did this so people would actually take interest in them).
So people ask me, "then why aren't those people in the Guru Granth Sahib as well," well the answer to it is, they were. The main people whose writings were responsible for the formation of the Guru Granth Sahib were Baba Kabir, Baba Farid GanShaker, and Guru Nanak.
I mentioned 3 sufi's and 2/3 were PROVEN Muslims (Baba Kabir and Baba Farid). Then people love asking me this "well then there were other Sufi's during Nanak's time and after his time as well, how come those weren't included in the Granth?
Well yea that's right there was Baba Bulleh Shah, Baba Sultan Bahu, and Baba Shah Hussain. Well they weren't given much attention by Hindus because THEY WERE NOT HINDUS, Guru Nanak at a point in his life WAS A HINDU, that's why Guru Nanak caught their attention the most.
His writings along with Kabir's writings along with Farid's writings come together to be compiled into a book called "Guru Granth Sahib" which ended after the writings of the 9th Guru (Guru Teg Bahadour).
My basic message is this, obviously while compiling the Guru Granth Sahib, religion was not looked upon as how this Holy Book was to be written since Hindu’s, Muslims, and Sikhs have contributed to it. So with that said and done, I say that it IS A POSSIBILITY that Guru Nanak could have been a Muslim (don’t get angry, Sikhs) but that’s for every each individual to decide.
I’ve already proven that he was not a Sikh (since there WAS no Sikhism at the time). So, for the Muslims I would say “try not to put the Sikhs down” by coming up with some lies (like saying Guru Nanak was married to a Muslim Woman) and for the Sikhs I would say “Try not to let your pride get in the way, if you respect the Gurus then according to the the laws of the Guru Granth Sahib you have to accept the Muslim bhagats as well and Guru Nanak just COULD have been one.
It’s now just a matter of opinion since even during Guru Nanak’s leaving to the heavens was a suspense (not cremated no buried) maybe that was the whole purpose.