Somewhere in Mahabharata Pandavas tell to Gandharvas that Ganga river can get served at any time and there are no rules for Ganga to get service like other rivers.
Please give those reference and the gist of the slokas.
This incident is mentioned in Mahabharata, Book 1: Adi Parva: Chaitraratha Parva: SECTION CLXXII when Pandavas were going towards Panchala after Lakshagriha incident. After travelling for many days when Pandavas arrived at the bank of river Ganga, at the same time a Gandharva named Angaraparna was sporting in that river with his family. But when Pandavas arrived there he became angry and frightened them.
Then those tigers among men, the sons of Pandu, arrived at the banks of the Ganga. Dhananjaya, that mighty car-warrior, walking before them, torch in hand, for showing the way and guarding them (against wild animals). And it so happened that at that time the proud king of the Gandharvas, with his wives, was sporting in that solitary region in the delightful waters of the Ganga. The king of the Gandharvas heard the tread of the Pandavas as they approached the river. On hearing the sounds of their foot-steps, the mighty Gandharvas were inflamed with wrath, and beholding those chastisers of foes, the Pandavas, approach towards him with their mother, he drew his frightful bow to a circle and said, 'It is known that excepting the first forty seconds the grey twilight preceding nightfall hath been appointed for the wandering of the Yakshas, the Gandharvas and the Rakshasas, all of whom are capable of going everywhere at will. The rest of the time hath been appointed for man to do his work. If therefore, men, wandering during those moments from greed of gain, come near us, both we and the Rakshasas slay those fools. Therefore, persons acquainted with the Vedas never applaud those men--not even kings at the head of their troops--who approach any pools of water at such a time. Stay ye at a distance, and approach me not. Know ye not that I am bathing in the waters of the Bhagirathi? Know that I am Angaraparna the Gandharva, ever relying on my own strength! I am proud and haughty and am the friend of Kuvera. This my forest on the banks of the Ganga, where I sport to gratify all my senses, is called Angaraparna after my own name. Here neither gods, nor Kapalikas, nor Gandharvas nor Yakshas, can come. How dare ye approach me who am the brightest jewel on the diadem of Kuvera?'
After that Arjuna said these restrictions are not applied to Ganga river.
"Hearing these words of the Gandharva, Arjuna said, 'Blockhead, whether it be day, night, or twilight, who can bar others from the ocean, the sides of the Himalayas, and this river? O ranger of the skies, whether the stomach be empty or full, whether it is night or day, there is no special time for anybody to come to the Ganga--that foremost of all rivers. As regards ourselves endued with might, we care not when we disturb thee. Wicked being, those who are weak in fighting worship thee. This Ganga, issuing out of the golden peaks of Himavat, falleth into the waters of the ocean, being distributed into seven streams. They who drink the waters of these seven streams, viz., Ganga, Yamuna, Saraswati, Vitashtha, Sarayu, Gomati, and Gandaki, are, cleansed of all their sins. O Gandharva, this sacred Ganga again, flowing through the celestial region is called there the Alakananda, It hath again in the region of the Pitris become the Vaitarani, difficult of being crossed by sinners, and, Krishna-Dwaipayana himself hath said so. The auspicious and celestial river, capable of leading to heaven (them that touch its waters), is free from all dangers. Why dost thou then desire to bar us from it? This act of thine is not in consonance with eternal virtue. Disregarding thy words, why shall we not touch the sacred waters of the Bhagirathi free from all dangers and from which none can bar us?'