Arthashastra
"ब्राह्मण क्षत्रिय वैश्य शूद्र सैन्यानां तेजः प्राधान्यात् पूर्वं पूर्वं श्रेयः सम्नाहयितुम्" इत्य् आचार्याः ॥
My teacher says that of the armies composed of Bráhmans, Kshatriyas, Vaisyas, or Súdras, that which is mentioned first is, on account of bravery, better to be enlisted than the one subsequently mentioned in the order of enumeration.
english translation
"brAhmaNa kSatriya vaizya zUdra sainyAnAM tejaH prAdhAnyAt pUrvaM pUrvaM zreyaH samnAhayitum" ity AcAryAH ॥
hk transliteration by Sanscript