Old English berēafian (see be-, reave). The original sense was 'deprive of' in general.

• rob from Middle English:

  The words rob and robe come from the same ancient root, a word meaning ‘booty’—clothing would have been the kind of property stolen in a raid. To rob Peter to pay Paul is to take something away from one person to pay another. The expression probably refers to the apostles St Peter and St Paul, who in Christian art are often shown together as equals. Although the earliest examples feature robbery, other versions have cropped up over the centuries, such as unclothe Peter to pay Paul and borrow from Peter to pay Paul. The last example probably helped in the additional meaning ‘to pay off one debt only to incur another’. The Scottish and English reavers or reivers, who plundered each other across the border got their name from ‘to reave’, another form of the original word, and those who are bereaved (Old English) have also been robbed of something precious—bereft is the old form of the word. A rover (Middle English) was originally another form of the word, but to rove (Late Middle English) is a different word: it was originally a term in archery meaning ‘shoot at a casual mark of undetermined range’. This may be from dialect rave ‘to stray’, probably of Scandinavian origin.