On one occasion the Venerable Sāriputta and the Venerable Mahamoggallana and the Venerable Anuruddha were dwelling at Saketa in the Thornbush Grove. Then, in the evening, the Venerable Sāriputta and the Venerable Mahamoggallana emerged from seclusion, approached the Venerable Anuruddha, and exchanged greetings with him. When they had concluded their greetings and cordial talk, they sat down to one side, and the Venerable Sāriputta said to the Venerable Anuruddha:
“Friend Anuruddha, it is said, ‘A trainee, a trainee.’ In what way, friend, is one a trainee?”
“It is, friend, because one has partly developed the four establishments of mindfulness that one is a trainee. What four? Here, friends, a bhikkhu dwells contemplating the body in the body … feelings in feelings … mind in mind … phenomena in phenomena, ardent, clearly comprehending, mindful, having removed covetousness and displeasure in regard to the world. It is because one has partly developed these four establishments of mindfulness that one is a trainee.”