SB 9.6.27

rājā tad-yajña-sadanaṁ
 praviṣṭo niśi tarṣitaḥ
dṛṣṭvā śayānān viprāṁs tān
 papau mantra-jalaṁ svayam
Synonyms: 
rājā — the King (Yuvanāśva); tat-yajña-sadanam — the arena of sacrifice; praviṣṭaḥ — entered; niśi — at night; tarṣitaḥ — being thirsty; dṛṣṭvā — seeing; śayānān — lying down; viprān — all the brāhmaṇas; tān — all of them; papau — drank; mantra-jalam — water sanctified by mantras; svayam — personally.
Translation: 
Being thirsty one night, the King entered the arena of sacrifice, and when he saw all the brāhmaṇas lying down, he personally drank the sanctified water meant to be drunk by his wife.
Purport: 

Yajñas performed by brāhmaṇas according to Vedic ritualistic ceremonies are so potent that the sanctifying of water by Vedic mantras can bring about the desired result. In this instance, the brāhmaṇas sanctified the water so that the King’s wife might drink it in the yajña, but by providence the King himself went there at night and, being thirsty, drank the water.