Shiva Purana
एताभ्यां खलु बालाभ्यां शिवपूजाविधीयताम् ॥ उपवीतानन्तरं हि शिवः श्रेयः करिष्यति ॥ ६१ ॥
Let the worship of Śiva be performed by these two sons. Only after the investiture with the sacred thread will Śiva bestow glory.
english translation
etAbhyAM khalu bAlAbhyAM zivapUjAvidhIyatAm ॥ upavItAnantaraM hi zivaH zreyaH kariSyati ॥ 61 ॥
hk transliteration by Sanscript