Shiva Purana
अथवा ऽहरहर्मंत्रं जपेदेकाग्रमानसः ॥ अनश्नन्नेव साहस्रं विना मन्त्रस्य साधनम् ॥ २४ ॥
Or he shall perform the Japa of the mantra a thousand times everyday, with full concentration of the mind. He shall not take food before the thousand Japas are completed.
english translation
athavA 'haraharmaMtraM japedekAgramAnasaH ॥ anaznanneva sAhasraM vinA mantrasya sAdhanam ॥ 24 ॥
hk transliteration by Sanscript