Canto 1 - Boyhood
Bāla-kāṇḍa
Chapter 12: Preparation for the Aśvamedha Sacrifice
Text 1.12.2

ततः प्रसाद्य शिरसा तं विप्रं देववर्णितम्।
यज्ञाय वरयामास सन्तानार्थं कुलस्य च॥

tataḥ prasādya śirasā taṁ vipraṁ deva-varṇitam
yajñāya
varayām āsa santānārthaṁ kulasya ca

tataḥ = then; prasādya = and offering obeisances unto; śirasā = bowing down his head; tam = that; vipram = brāhmaṇa Ṛśyaśṛṅga; deva-varṇitam = of celestial luster; yajñāya varayām āsa = Daśaratha accepted him to perform the yajña; santāna-artham = to have sons; kulasya ca = to continue his dynasty.

Then, bowing down his head and offering obeisances unto that brāhmaṇa Ṛśyaśṛṅga of celestial luster, [Daśaratha] accepted him to perform the yajña to have sons to continue his dynasty.

When Daśaratha had to accept a sacrificial priest to perform the Sāṅgrahaṇī Iṣṭi, he first accepted Ṛśyaśṛṅga as the Brahmā priest for the sacrifice. That is noted here.