Shiva Purana
उत्तमं मानसं जाप्यमुपांशुं चैवमध्यमम् ॥ अधमं वाचिकं प्राहुरागमार्थविशारदाः ॥ २४ ॥
Experts in the meanings of Āgama texts say that the mental Japa is excellent, the Upāṃśu Japa (in a low voice) is the middling. The verbal Japa is of the lowest quality.
english translation
uttamaM mAnasaM jApyamupAMzuM caivamadhyamam ॥ adhamaM vAcikaM prAhurAgamArthavizAradAH ॥ 24 ॥
hk transliteration by Sanscript