Iramanuja Nootrandadi

thiuvarangathu amudhanAr was previously known as periya kOil nambi. He was the official guardian of srI rangam temple and was doing purOhithyam (reading purANam, vEdha viNNappam, etc). Initially, he was not favourable towards emperumAnAr‘s efforts to reform the activities in the temple. But, by the divine grace of srIman nArAyaNan, he ultimately got the relationship with emperumAnAr and benedicted.
After some time, amudhanAr writes rAmAnusa nURRanthAdhi (108 pAsurams) on emperumAnAr and submits that to emperumAn and emperumAnAr. namperumAL, once during the last day of brahmOthsavam orders emperumAnAr not to accompany him in the procession and asks the srIvaishNavas to recite rAmAnusa nURRanthAdhi during the procession - which eventually becomes a routine to be followed during every uthsavam. Understanding emperumAn’s desire, emperumAnAr himself acknowledges this great work of amudhanAr and includes that as part of iyaRpA similar to how kaNNinuN chiru thAmbu of madhurakavi AzhwAr(which glorifies nammAzhwAr) is included in mudhalAyiram. This prabhandham becomes to be famously known as prapanna gAyathri and emperumAnAr also instructs all srIvaishNavas to recite this prabhandham atleast once every day similar to gAyathri japam being mandatorily recited everyday by the ones who have undergone brahmOpadhEsam (the ones who wear the yagyOpavItham - sacred thread).