Already fossilized as early as Proto-Italic as po- in words like poner.
From Proto-Indo-European *h2p-o 'id.' From the full grade *h2epo "away" (see ab-)
Old High German fane "from," Old Frisian fan 'id.,' Old Saxon fan 'id.'
Albanian pa "without"
Old Church Slavonic po "after," "by," Russian po 'id.,' Czech po 'id.,' Bulgarian po 'id.' Lithuanian po-, a perfective-forming prefix
de Vaan, M.
Etymological Dictionary of Latin and Other Italic Languages.
Real Academia Española.
Diccionario de la lengua española.
Online. 23rd ed. Madrid: Espasa Calpa.