Manusmriti
तेषां त्रयाणां शुश्रूषा परमं तप उच्यते । न तैरनभ्यनुज्ञातो धर्ममन्यं समाचरेत् ॥ २२९ ॥
Obedience towards those three is declared to be the best (form of) austerity; let him not perform other meritorious acts without their permission.
english translation
teSAM trayANAM zuzrUSA paramaM tapa ucyate । na tairanabhyanujJAto dharmamanyaM samAcaret ॥ 229 ॥
hk transliteration by Sanscript