Matsya Purana 249.55

249.55

tataḥ śrāntāstu te sarve devāḥ daityapuraḥ saraḥ.
śrānteṣu teṣu devendro megho bhūtvāmbuśīkarān .. 249.55 ..

When all the Devas and the demons were overcome with fatigue in churning the ocean, Indra caused the rains and cool wind to refresh them But, in spite of all that when the Lord Brahmâ found them giving way to fatigue, He shouted out “Go on churning Those who persevere are undoubtedly blessed with the highest prosperity” —55 57