Śrīmad-Bhāgavatam · Text 5.17.9
Who is speaking and story frame
तथैवालकनन्दा दक्षिणेन ब्रह्मसदनाद्बहूनि गिरिकूटान्यतिक्रम्य हेमकूटाद्धैमकूटान्यतिरभसतररंहसा लुठयन्ती भारतमभिवर्षं दक्षिणस्यां दिशि जलधिमभिप्रविशति यस्यां स्नानार्थं चागच्छत: पुंस: पदे पदेऽश्वमेधराजसूयादीनां फलं न दुर्लभमिति ॥ ९ ॥
tathaivālakanandā dakṣiṇena brahma-sadanād bahūni giri-kūṭāny atikramya hemakūṭād dhaimakūṭāny ati-rabhasatara-raṁhasā luṭhayantī bhāratam abhivarṣaṁ dakṣiṇasyāṁ diśi jaladhim abhipraviśati yasyāṁ snānārthaṁ cāgacchataḥ puṁsaḥ pade pade ’śvamedha-rājasūyādīnāṁ phalaṁ na durlabham iti.
Similarly, the branch of the Ganges known as Alakanandā flows from the southern side of Brahmapurī [Brahma-sadana]. Passing over the tops of mountains in various lands, it falls down with fierce force upon the peaks of the mountains Hemakūṭa and Himakūṭa. After inundating the tops of those mountains, the Ganges falls down onto the tract of land known as Bhārata-varṣa, which she also inundates. Then the Ganges flows into the ocean of salt water in the south. Persons who come to bathe in this river are fortunate. It is not very difficult for them to achieve with every step the results of performing great sacrifices like the Rājasūya and Aśvamedha yajñas.
Read Śrīla Prabhupāda's purport on Vedabase.io