Mbh 1.134.4

“Thus Drona continued giving lessons to the princes in the science of weapons. And while he gave unto every one of his pupils a narrow-mouthed vessel (for fetching water) in order that much time may be spent in filling them, he gave unto his own son Aswatthaman a broad-mouthed vessel, so that, filling it quickly, he might return soon enough. And in the intervals so gained, Drona used to instruct his own son in several superior methods (of using weapons). Jishnu (Arjuna) came to know of this, and thereupon filling his narrow-mouthed vessel with water by means of the Varuna weapon he used to come unto his preceptor at the same time with his preceptor’s son. And accordingly the intelligent son of Pritha, that foremost of all men possessing a knowledge of weapons, had no inferiority to his preceptor’s son in respect of excellence. Arjuna’s devotion to the service of his preceptor as also to arms was very great and he soon became the favourite of his preceptor. And Drona, beholding his pupil’s devotion to arms, summoned the cook, and told him in secret, ‘Never give Arjuna his food in the dark, nor tell him that I have told thee this.’ A few days after, however, when Arjuna was taking his food, a wind arose, and thereupon the lamp that had been burning went out. But Arjuna, endued with energy, continued eating in the dark, his hand, from habit, going to his mouth. His attention being thus called to the force of habit, the strong-armed son of Pandu set his heart upon practising with his bow in the night. And, O Bharata, Drona, hearing the twang of his bowstring in the night, came to him, and clasping him, said, ‘Truly do I tell thee that I shall do that unto thee by which there shall not be an archer equal to thee in this world.’