Answer: There was a lot of conflict between the Sunni and Shi'ite Muslims.
Step-by-step explanation:
Both the Ottoman and the Safavid empires were Muslim empires that came to prominence around the same time. The Ottomans were very worried about rising Safavid influence and sought to check it.
Islamic law did not however, allow Muslims to go to war against each other without religious justification and so the Ottomans labeled Shi'ite Islam to be heretic as they were Sunni. This became a major source of conflict between the two empires that saw multiple wars fought.