Dr. Muhammad M. Abu Laylah, professor of Islamic Studies and Comparative Religions at Al-Azhar University, states the following:
"Sikhism is a very recent sect although its adherents call it a religion. The founder of Sikhism is Guru Nanak Dev Ji, who took materials and principles from Hinduism, Buddhism and Islam and perhaps from other religions.
The founder of this sect was very close to Islam. It is said that he visited Makkah and to a certain degree some people thought that he was approaching Islam at the very beginning.
Sikhism is widespread in India, and Sikhs have large communities in England and America. They offer their worship in the same way as Hindus do (i.e., in a temple). They have a Holy Book, and they take care of it by putting it in a special way inside their temples. Their tradition is close to the Hindu tradition. Some Hindu priests leave their hair uncut and wear a bracelet around their wrists. Some baptized people from among the Sikhs are required to keep their hair uncut.
We consider Sikhism as a tradition rather than a religion. Sikhs are trying to fight for independence from India and to have their own independent state. They stand by some values, which brings them close to Islam and other religions. But we do not acknowledge any religion after Islam.
Islam acknowledges that Allah sent a Prophet to every nation and that every Prophet spoke the same language that was widespread among the people he was sent to. There is no direct indication in the Qur’an or the Sunnah about Hinduism, Buddhism or Sikhism. However, there are many common elements between such sects and polytheism. Also, there are many misconceptions regarding God, and those misconceptions are shared between Sikhism and polytheism.
The core of the Hindu religion is reincarnation, i.e., that man has many lives and he can appear in the shape of another man or an animal to suffer or to enjoy according to his deeds and works in his previous life.
It is needless to say here that the doctrine of reincarnation is totally rejected in Islam. The Hindus also believe in Nirvana, i.e., that the good righteous people are embodied in god, and this is also entirely rejected in Islam. We believe that righteous people will enter Paradise as a reward for their righteousness.
Having stated the above, I would like to add that the Indians have their rich and abundant traditions like Muslims, and many Indians stick to basic human values. They have many wise and religious people. That is why Muslim scholars benefit from their culture like Kalilah Wa Dimnah that were translated by Ibn Al-Muqaffa`. We can trace some wise sayings in the Arabic sources back to their Indian origins. But we should guard ourselves against polytheism demonstrated in the “godhead” that is unique in the Indian religions.
When Islam entered India, the Indians were free to practice their religions and lead their lives according to their traditions. The Muslim rulers never compelled anyone of them to accept Islam or to change his identity or to detest his way of life.
It is useful here to refer you to Al-Biruni’s book “Tahqiq Ma lilhind min Maqulah Maqbulah fi Al-`Aql wa Mardhulah”, which is available in both Arabic and English. In it, Al-Biruni clearly reviews the Indian history and civilization in a critical and academic way."