Canto 1 - Boyhood
Bāla-kāṇḍa
Chapter 44: Bhagīratha Delivers his Uncles
Text 1.44.7

पितामहानां सर्वेषां त्वमत्र मनुजाधिप।
कुरुष्व सलिलं राजन्प्रतिज्ञामपवर्जय॥

pitāmahānāṁ sarveṣāṁ tvam atra manujādhipa
kuruṣva
salilaṁ rājan pratijñām apavarjaya

pitāmahānām = of your grandfathers; sarveṣām = for all; tvam atra = here; manuja-adhipa = O Lord of men; kuruṣva = perform; salilam = the final rites; rājan = O king; pratijñām = the promise [you had made]; apavarjaya = fulfill.

O Lord of men, O king, perform the final rites for all of your grandfathers here. Fulfill the promise [you had made].

Bhagīratha had promised that he would perform the final rites for the sons of Sagara with the water of Gaṅgā and thus deliver them [from their ghostlike existence]. Lord Brahmā wanted Bhagīratha to fulfill his promise.