Step 1: Identify the Alvars:
The Alvars were a group of South Indian Tamil poet-saints (c. 6th-9th century CE) devoted to Vishnu, composing hymns later collected as the 'Nalayira Divya Prabandham'.
Step 2: Classify their tradition:
Their devotion centred on Vishnu and his avatars, placing them within the Vaishnava bhakti tradition (as distinct from the Shaiva Nayanars).
Final Answer:
\[ \boxed{\text{Vaishnava religion}} \]