Manusmriti
अनेन विधिना यस्तु गोघ्नो गामनुगच्छति । स गोहत्याकृतं पापं त्रिभिर्मासैर्व्यपोहति ॥ ११५ ॥
The slayer of a cow who serves cows in this manner, removes after three months the guilt which he incurred by killing a cow.
english translation
anena vidhinA yastu goghno gAmanugacchati । sa gohatyAkRtaM pApaM tribhirmAsairvyapohati ॥ 115 ॥
hk transliteration by Sanscript