Shiva Purana
उद्धूलनं त्रिपुंड्रं च श्रद्धया नाचरन्ति ये । ते महापातकैर्युक्ता इति शास्त्रीयनिर्णयः १६ ।
This is the final conclusion of all sacred texts that those who do not observe with faith Tripuṇḍra and Uddhūlana are tarnished by great sins.
english translation
uddhUlanaM tripuMDraM ca zraddhayA nAcaranti ye । te mahApAtakairyuktA iti zAstrIyanirNayaH 16 ।
hk transliteration by Sanscript