These forty-nine fire-gods are the beneficiaries of the oblations offered in the Vedic sacrificial fire by impersonalist brāhmaṇas.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
वैतानिके कर्मणि यन्नामभिर्ब्रह्मवादिभिः । आग्नेय्य इष्टयो यज्ञे निरूप्यन्तेऽग्नयस्तु ते
vaitānike karmaṇi yannāmabhirbrahmavādibhiḥ | āgneyya iṣṭayo yajñe nirūpyante'gnayastu te
SB 4.1.62