Pathanjali Yoga sutra
Yoga is neither for atheism nor for theism. It is a natural simple science.
Pathanjali is a unique personality with his miraculous ways. He never defines any relation with Eshwara. Though there are references to Eshwara at moments, he still defines Eshwara as one of the means to attain the ultimate truth. Having faith in Eshwara is mearly a techinique. There is a possibility of prayer and surrender as well. The greatness is about prayer and surrender. Pathanjali is an extraordinary individual.
He gives importance to Eshwar pranidhana as one of the methodologies to get to the truth - a way and not renunciation. No matter your choice, faith will lead the intellect to eternity. His choice is unique. There is no need for Eshwar himself, for Eshwar is not the ultimate goal. Patanjali neither rejects nor suspects. He is a complete scientist. The most difficult fact for Hindus is to know how Mahaveera or Buddha attained salvation. This is because Mahaveera never had faith in Eshwara.
There was always an inherited way to get to the truth which was void of Eshwara. This made the Hindus anxious as it absolutely contradicted the eastern thought of getting to the ultimate truth. According to Pathanjali, we need not become entangled by any dogmas. Tools and techniques are many, but truth is the one and only goal. Many have attained truth through Eshwara. Which is, of course, one of the right ways, for even faith in Shiva will lead you to truth.
But once you get to the truth, you may discard the faith in Shiva. Hence faith in itself is simply a tool. What is important is to reach the goal. Hence Pathanjali is neither an atheist nor a theist. Pathanjali is a saint. He is not establishing any religion. He is only showing us different paths, possibilities, and disciplines. You are free to choose what facilitates your transformation. In all these different paths, Eshwara is one of the paths. Just because Eshwara is one of the paths does not mean it is a mandatory path. If you do not have faith in Eshwara, you need not be non-religious. Pathanjali says you can get to the truth though you do not have faith in Eshwara. You need not think about Eshwara. Pathanjali does not particularly emphasize any specific ideology. Hence Pathanjali's Yogasutra is one of its kind - with no precedence and no possibility of anything similar in the future.
Anything and everything has already been written by him and there is nothing beyond this in yoga. There is nothing to be added or removed from here. He has concluded this with utmost completeness. Buddha, Jesus, Mohammed, and Mahaveer - each of them trod their own paths. Each had their own distinct and definite ways. Such a distinction is created with compassion by these leaders only for the sake of creating better interest and convenience for the masses, who tended to lace passion with these paths to the truth. Though leaders like Ramnuja Madhavacharya and Shankaracharya knew that all paths lead to the same ultimate truth, different paths were created to generate passion amongst the people. In other words they were compelled to bring in this distinction.
For example, Basavanna said that Eshwara is the only means to get to the truth. However, what needs to be noted is that this was told not to mislead the people, but was a trick to generate passion among the masses. The common man is ever suspicious. Hence it would be very confusing for them to understand that all paths lead to the truth. Hence in order to help their focus, Basavanna was forced to call out that Eshwara to be the only path. Pathanjali is unattached to anyone. His relationship with you is very rare. He has a greater relationship with the creation of these methodologies. He does not experiment on strategies or what is untrue. He does not seek your agreement. On the contrary, Buddha was extremely compassionate and humanitarian, and in order to get you to the truth, he might not hesitate to agree with you. Pathanjali is exceptional, unreasonable, and unusually just. Pathanjali presents truth in its blunt form.
He would not descend just for the sake of coming to terms with you. He does not weave any stories to deliver the message. His intent was straight and to the point. Pathanjali's Yogasutra does not provide any comfort, but rather, is the presentation of truth in its naked form. While Buddha was a theist and Einstein was atheist, Pathanjali was neither.
An example: When a calamity struck, the villagers went to a saint to save them. The saint chanted a mantra, performed a sacrifice, and prayed for the well-being of the villagers, “Let the people be freed from their miseries and be happy", and the villagers were blessed.
After a few years, in a similar situation, the villagers once again went looking for the old saint. The old saint was gone but found another saint. This saint chanted a different mantra, performed different sacrifices, and prayed for the well-being of the people, “Let the people be freed from their miseries and stay happy.” A similar calamity struck a third time, but now, the villagers could not find a saint, so they went to a modern guru. The guru did not chant any mantras, nor perform any sacrifices, but simply prayed for the well-being of the people, “Let the people be freed from their miseries and remain happy.”
The villagers were blessed. While all the three prayed for the same well-being, their approaches were different. Only their intention was common. Pathanjali Yogasutra is only about the final intent, and not about the different means to get there.