One of the first and closest followers of Guru Nanak, who was with him most of his life, was Bhai Mardana. And even today, many pictures of Guru Nanak would have Bhai Mardana in them. Guru Nanak famously, as someone who was spiritually precocious and spiritually curious, traveled through India and Persia and the Middle East, so he visited many temples, but there's also many historic accounts of him going to Mecca and performing hajj. The Guru Granth Sahib, which is considered the spiritual book, the 11th and final Guru for the Sikhs, of the contributors to them, you have Kabir, who grew up in a Muslim family. He lived either around the time of Guru Nanak or in the century before Guru Nanak and would write about both Allah and Ram, although he was often critical of both Hinduism and Islam. And you also have Sheikh Farid, who was a Muslim Sufi writer and spiritual figure, and he has also contributed to the Guru Granth Sahib. There's also important rituals that come from Hinduism.