sikhism is not a religion but way and teaching to live in this planet being a part of the universel play .guru nanak is the only undisputed essance in the universe equally respected by all forms of life,people and religions.there has been disputes and suggetions on any other bodily soul ever eisting on planet earth but the wonderful way of guru nanaks life has been an example for all other souls in human form to stay as a guest here and behave and act as a guest of the kings of kings as anyone would in a kings palace.then u have to depart and go back home to your loved one and actual home.guru nanak is god himself and there is no instace or trace anywhere in his life where he believed in any religion.