Srimad-Bhagavatam: Canto 10 - Chapter 1 - Verse 6

Sanskrit:

श्रीशुक उवाचइत्युक्त्वा यज्ञिये काले वव्रे युक्तान् स ऋत्विज: ।कृष्णानुमोदित: पार्थो ब्राह्मणान् ब्रह्मवादिन: ॥ ६ ॥

ITRANS:

śrī-śuka uvācaity uktvā yajñiye kālevavre yuktān sa ṛtvijaḥkṛṣṇānumoditaḥ pārthobrāhmaṇān brahma-vādinaḥ

Translation:

Śukadeva Gosvāmī said: Having said this, King Yudhiṣṭhira waited until the proper time for the sacrifice was at hand. Then with Lord Kṛṣṇa’s permission he selected suitable priests, all expert authorities on the Vedas, to execute the sacrifice.

Purport:

The great Bhāgavatam commentator Śrīdhara Svāmī explains that the proper time for the sacrifice mentioned here was the spring.