स य एवमेतद्रथंतरमग्नौ प्रोतं वेद ब्रह्मवर्चस्यन्नादो भवति सर्वमायुरेति ज्योग्जीवति महान्प्रजया पशुभिर्भवति महान्कीर्त्या न प्रत्यङ्ङग्निमाचामेन्न निष्ठीवेत्तद्व्रतम् ॥ २.१२.२ ॥
In plain words
He who knows the Rathantara chant thus woven upon fire becomes lustrous with the light of Brahman and an eater of food, reaches his full span of life, lives long, becomes great in offspring and cattle, great in renown. Let him not rinse his mouth facing the fire, nor spit toward it: that is the vow.