Shiva Purana
पुष्पहस्तो जपेच्छक्त्या मन्त्रं मन्त्रविशुद्धये ॥ ऐशान्यां चण्दमाराध्य निर्माल्यं तस्य दापयेत् ॥ २१ ॥
Holding a flower in his hand, one should chant the mantra with all his might to purify the mantra. One should worship the moon in the northeast and offer him a garland.
english translation
puSpahasto japecchaktyA mantraM mantravizuddhaye ॥ aizAnyAM caNdamArAdhya nirmAlyaM tasya dApayet ॥ 21 ॥
hk transliteration by Sanscript