The Satadhusani is a work by the Sri Vaishnava Acharya Vedanta Desikan consisting of 100 refutations of Adi Shankaracharya's philosophy of Advaita. One chapter of the work is devoted to refuting Advaita beliefs about Sanyasa. Advaitins believe that Sanyasis should discard their Yajnopavita or sacred thread, cut off their Shikha or tuft of hair, and walk around with an Ekadanda or single rod. Sri Vaishnavas, in contrast, believe that Sanyasis should keep their sacred thread and Shikha, and walk around with a Tridanda or bundle of three rods.
Now one of the Advaita arguments Vedanta Desikan refutes is the argument that Advaita practices of Sanyasa should be followed because they have been followed by good people in the past. Here is how Vedanta Desikan responds to that:
It cannot be [valid], because (a) mere custom that goes against Vedic and other authoritative statements is inadmissible; (b) we do not find the abandonment of the sacrificial cord in the Puranic eulogies of renouncers such as Panchashikha and Durvasa; (c) we do not hear of its abandonment by [Arjuna] and others who imitated the conduct of renouncers; (d) this practice lacks the quality of a (true) custom that one should conform to, because the lineage of Bhaskaracharya, Yadavaprakasha, and Blessed Nathamuni, who belonged to your group, has been broken, and because of the sum of disagreements that has been introduced into your faction.
I'm interested in the part in bold. The translator says "Many former Advaita renouncers, such as those mentioned, have repudiated this Advaita custom." So that means these three figures were originally Advaita-style Ekadandi Sanyasis and then they repudiated this practices later on.
Now Bhaskaracharya is the author of the second-oldest commentary on the Brahma Sutras. He subscribed to a philosophy called Aupadhika Bhedabheda, and he's known for his critiques of Ekadandi Sanyasa, though I didn't know that he started out as an Ekadandi Sanyasi himself. Yadavaprakasha was the original guru of Ramanujacharya, and he subscribed to a philosophy called Svabhavika Bhedabheda. Ramanujacharya left Yadavaprakasha and became a Sri Vaishnava, and then later on Yadava Prakasha converted to Sri Vaishnavism and became Ramanujacharya's shishya! In the process, Yadava Prakasha switched from being an Ekadandi Sanyasi to a Tridandi Sanyasa, and he even wrote a manual describing the correct practices for Sri Vaishnava Sanyasis.
But I'm interested in the third figure mentioned, Nathamuni. For those who don't know, Nathamuni was an important Sri Vaishnava Acharya. He was the one who compiled the Alwars' poems into Naalaayira Divya Prabandham, and he codified the beliefs and principles embodied into the Alwars' poems into what we now call Sri Vaishnavism and Visistadvaita. My question is, before Nathamuni became a Sri Vaishnava, was he an Ekadandi Sanyasi? If so who was his original guru who initiated him into Sanyasa, and what sect of Hinduism did that guru belong to?