Sheik Farid's bani is in SGGS. Bhagat Bhikhan also has two hymns in SGGS. The man who laid the cornerstone of the Golden Temple was a Pir as well. His name was Hazrat Mian Mir and he was beloved of Guru Arjan Dev Ji.
Our Guru says to associate with those who chant the name of God and serve those who serve the saints. It does not discriminate between any religion and any other religion. All paths lead to the same mountaintop. All rivers eventually flow into the same ocean.
ANG 1167 Siri Guru Granth Sahib Ji: Bhagat Naam Dev
Come, O Lord of beautiful hair, wearing the robes of a Sufi Saint.
Your cap is the realm of the Akaashic ethers; the seven nether worlds are Your sandals.
The body covered with skin is Your temple; You are so beautiful, O Lord of the World.
The fifty-six million clouds are Your gowns, the 16,000 milkmaids are your skirts.
The eighteen loads of vegetation is Your stick, and all the world is Your plate.
The human body is the mosque, and the mind is the priest, who peacefully leads the prayer.
You are married to Maya, O Formless Lord, and so You have taken form.
Performing devotional worship services to You, my cymbals were taken away; unto whom should I complain?
Naam Dev’s Lord and Master, the Inner-knower, the Searcher of hearts, wanders everywhere; He has no specific home.
