( Story told by Swami Vivekananda )
There is a story of Hanumân, who was a great worshipper of Râma. Just as the Christians worship Christ as the incarnation of God, so the Hindus worship many incarnations of God. According to them, God came nine times in India and will come once more. When he came as Rama, this Hanuman was his great worshipper. Hanuman lived very long and was a great Yogi.
During his lifetime, Rama came again as Krishna; and Hanuman, being a great Yogi, knew that the same God had come back again as Krishna. He came and served Krishna, but he said to him, “I want to see that Rama form of yours”. Krishna said, “Is not this form enough? I am this Krishna; I am this Rama. All these forms are mine”. Hanuman said, “I know that, but the Rama form is for me. The Lord of Jânaki (Janaki is a name of Sitâ.) and the Lord of Shri ( Shri is a name of Laksmi.) are the same. They are both the incarnations of the Supreme Self. Yet the lotus-eyed Rama is my all in all”. This is Nishtha — knowing that all these different forms of worship are right, yet sticking to one and rejecting the others. We must not worship the others at all; we must not hate or criticize them, but respect them.
Source: The Complete Works of Swami Vivekananda/Volume 9/Lectures and Discourses/Bhakti-Yoga