As I discuss in this answer, one of the early movements that was important in the development of Vaishnavism was the ancient Pancharatra movement, whose sacred texts consist of detailed procedures to worship the sage Narayana, an ancient incarnation of Vishnu who was the son of Yama god of death and twin brother of the sage Nara. Among the oldest Pancharatra texts are the Satvata Samhita, Paushkara Samhita, and Jayakhya Samhita. But there is another Pancharatra text even older than those, and it's found within the Shanti Parva of the Mahabharata! It's called the Narayaniya, and it is an 18-chapter religious dialogue between Yudishthira and Bhishma, similar to the Bhagavad Gita, another 18-chapter religious discourse between Krishna and Arjuna found in the Bhishma Parva of the Mahabharata.
In any case, this chapter of the Narayaniya section describes how three sages who were brothers, named Ekata, Dwita, and Trita, decided to go to the White Island in the middle of Vishnu's ocean of milk in order to see Vishnu. They engaged in Tapasya for a long time, but Vishnu didn't appear before him. Finally, Vishnu spoke to them as an invisible voice, and told them only those with true devotion could see him:
Go hence, ye Munis, to the place whence ye have come. That great Deity is incapable of being ever seen by one that is destitute of devotion. Incapable of being seen in consequence of his dazzling effulgence, that illustrious Deity can be beheld by only those persons that in course of long ages succeed in devoting themselves wholly and solely to Him. Ye foremost of regenerate one, ye have a great duty to per-form. After the expiration of this the Krita age, when the Treta age comes in course of the Vivaswat cycle [Manvantara], a great calamity will overtake the worlds. Ye Munis, ye shall then have to become the allies of the deities (for dispelling that calamity).
My question is, how did Ekata, Dwita, and Trita help the gods overcome "a great calamity" in a Treta Yuga of the Vaivasvata Manavantara? We are currently living in the 28th Kali Yuga of the Vaivasvata Manvantara, so this must have happened some time in the present Manvantara.
The only story I've heard involving these three sages is the story of how Trita was abandoned in a well by his brothers Ekata and Dwita, and got himself out by performing a Yagna in the bottom of the well, as described in this chapter of the Shalya Parva of the Mahabharata. (It's also alluded to in this hymn of the Rig Veda, which was heard from the gods by Trita as you can see in my answer here.)
Does anyone know of any scriptures that describe them helping the gods in a time of calamity?