Valmiki Ramayana Ayodhya Kanda Sarga 30 Shloka 34

शुभापाङ्गे O one having lovely side glances, यत्र which, त्रयम् all the three (father, mother and preceptor), तत्र that, त्रयः three, लोकाः worlds, तत्समम् equal to those three, पवित्रम् अन्यत् any other holy thing, लोके in the world, नास्ति none, तेन therefore, इदम् this, अभिराध्यते is worshipped.

Where these three(mother,father and preceptor) equal to the three worlds are, O one with loverly sideglances, there is none in this world as holy. Therefore, they are to be worshipped.