Baba Guru Nanak’s birth anniversary celebrations begin from Nov 7
Baba Guru Nanak was a Muslim Saint- Hazrat Mirza Tahir Ahmad(rh) the 4th caliph of Ahmadiyya Muslim Community answers a question by a Sikh about the faith of Hazrat Guru Baba Nanak whom the Sikhs believe to be the founder of the Sikh faith.
http://www.youtube.com/watch?v=nOzNbCPj70Y
The proofs are that Hazrat Guru Nanak had his own personal pocket size copy of Quran, he travelled to Mecca and performed Hajj. The Chola Baba Nanak which is considered to be a holy relic has Quran verses and prayers written all over it. Hazrat Mirza Tahir Ahmad(rh) explains how the Sikh faith become a separate faith, it was more of a political struggle of Punjab against the then Mughal Emperor Aurangzeb who wished to gain more strength in Punjab, it resulted in a backlash against the Emperor and a dissatisfaction against Islam.

It is true that Baba Guru Nanak was a high level Muslim. He went to Makkah for Hajj. He was followers of Muslim Sufi. He was a great leader and he believed in One God. He was monotheist.
Hindus did not like Baba Guru Nanak sahib. Where ever Baba Jee sat down, the Hindus considered that place as dirty and they used to wash that place with the cow’s dung to make the place pawitter (holy, clean).
It was the Muslim Mullas who spoiled the show. Ignorant Mullas tried to strictly apply the laws of Fiqah on the followers (New Muslims) of Baba jee. That made the followers to distance themselves away from Islam.
The Sikhs are brave nation. They work hard and earn money and spend it the way of their faith. We have never seen any Sikh begging or begger. I suggest that all Sikhs should try to read the Quran. That is what Baba Jee did. In that way the Sikh will be true followers of Baba Guru Nanak Jee.