Shloka 2.21.23
अयोध्याकाण्डे एकविंशः सर्गः — Lakṣmaṇa’s militant counsel and Rāma’s dharma-based persuasion of Kausalyā
शुश्रूषुर्जननीं पुत्र स्वगृहे नियतो वसन्।परेण तपसा युक्तः काश्यपस्त्रिदिवं गतः।।2.21.23।।
śuśrūṣur jananīṃ putra svagṛhe niyato vasan | pareṇa tapasā yuktaḥ kāśyapas tridivaṃ gataḥ || 2.21.23 ||
O son, by living with discipline in his own home and serving his mother, Kāśyapa—endowed with supreme austerity—attained heaven.
O son! Kasyapa who led a life of self-discipline and served his mother at home, attained heaven credited with (the merit of) the highest penance.
Service to one’s mother is presented as a form of tapas (austerity) and a dharmic path that yields spiritual merit.
Kausalyā cites a traditional exemplar (Kāśyapa) to persuade Rāma that staying home and serving his mother is itself ‘highest penance’.
Self-discipline (niyama) combined with devoted service (śuśrūṣā).