In my reading I have learned that the Baha'i historically have taught that Christ was who he says he was and Muhammad is who he says he was. The Baha'i too subscribe, more so than Latter-day Saints that truth is truth wherever it can be found. They also seem to teach the concept of apostasy, though the word is not used as a label. The following passage, that I have found describes that truth , called the Sun of Reality.
The people of perception are the seekers of the truth, and not the places of its appearance, nor of its dawning points; therefore they will adore the Sun from whatever point in the zodiac it may appear, and they will seek the Reality of the Sanctified Soul Who manifests it. Such people always attain to the truth and are not veiled from the Sun of the Divine World.It goes on to describe how many religions that exist in the world today get "stuck" on the teachings of certain people.
"For example, once the Sun of Reality poured forth its ray from the sign of Abraham, and then it dawned from the sign of Moses and illuminated the horizon. Afterward it rose with the greatest power and brilliancy from the sign of Christ. Those who were seekers of Reality worshipped that Reality wherever they saw it, but those who were attached to Abraham were deprived of its influences when it shone upon Sinai and illuminated the reality of Moses. Those who held fast to Modeses, when the Sun of Reality shone from Christ with the utmost radiance and lordly splendor were also veiled; and so forth."In terminology reminiscent of the early LDS prohets:
"Therefore, man must be the seeker after the Reality and he will find that Reality in each of the Sanctified Souls. He must be fascinated and enraptured, and attracted to the divine bounty; he must be like the butterfly who is the lover of the light from whatever lamp it may shine, and like the nightingale who is the lover of the rose in whatever garden it may grow."It was this sort of logic that led me to ever begin learning about the LDS Church. I found a completeness of doctrine and was taught that "the reality" of existence began with the creation of the universe, we lived premortally and that the plan of salvation is not just a story concocted by humans to explain away our presence on the earth, but the explanation from the beginning of all that we see and experience.
One of the beauties of the "first principles and ordinances of the gospel" is that they are so simple, so universal and so accessible to all--if not in this life, in the next and time is given to extend those ordinances to each person who ever lives. But as I'm continuing on my individual "search for truth and meaning" I am feeling that as I have secured those blessings for myself, and strive to teach my children, friends and family to secure those blessings for themselves, that I must continue onward seeking truth wherever it can be found. I love the doctrines of the gospel, and yearn for the hidden treasures and mysteries, spoken of in the Word of Wisdom and the Book of Mormon. I'm finding that as I explore and seek out the doctrines of the gospel of Christ, I am finding portions that testify of the divine reality in many places, across religions.
I find this requires an open and inquisitive mind that when I find something where I instinctively recoil, I can objectively study it out to learn more. For example, I feel that my next steps are to learn about the prophet Mohammad and other spiritual leaders of other religions to decide for myself if they are, like the framers of the Protestant Reformers, inspired men and women who speak truth to a certain time, culture and people that can give them a foundation for seeking further truth and knowledge. I feel that the Unitarian Universalists did that for me and by being accepting enough to seek additional truth, I did find and now I can continue seeking and find more.