Valmiki Ramayana Bala Kanda Sarga 44 Shloka 9

तात O Child, तथैव similarly, लोके in this world, अप्रतिमतेजसा by the one possessing unparalleled prowess, गङ्गाम् Ganga, आनेतुम् for bringing, प्रार्थयता cherished, अंशुमता by Anshuman's, प्रतिज्ञा vow, नापवर्जिता could not be completed.

O Child similarly though Anshuman possessed unparalleled prowess in this world his prayer to Ganga, his vow could not be fulfilled.