At Sāvatthi.

"Bhikkhus, just as households with many women but few men are easily overwhelmed by thieves and burglars, so too, a bhikkhu whose release of mind through loving-kindness is undeveloped and uncultivated is easily overwhelmed by non-human beings. Conversely, just as households with few women but many men are hard to overcome by thieves and burglars, so too, a bhikkhu whose release of mind through loving-kindness is well-developed and cultivated is hard to overcome by non-human beings.

Therefore, bhikkhus, you should train yourselves thus: 'Our release of mind through loving-kindness will be developed, practiced often, made a vehicle, made a basis, firmly established, nurtured, and resolutely undertaken.' Thus, bhikkhus, you should train yourselves."