Lycurgus (15.7-15.8)

For example, an elderly man with a young wife, if he looked with favour and esteem on some fair and noble young man, might introduce him to her, and adopt her offspring by such a noble father as his own. And again, a worthy man who admired some woman for the fine children that she bore her husband and the modesty of her behaviour as a wife, might enjoy her favours, if her husband would consent, thus planting, as it were, in a soil of beautiful fruitage, and begetting for himself noble sons, who would have the blood of noble men in their veins.

For in the first place, Lycurgus did not regard sons as the peculiar property of their fathers, but rather as the common property of the state, and therefore would not have his citizens spring from random parentage, but from the best there was. In the second place, he saw much folly and vanity in what other peoples enacted for the regulation of these matters; in the breeding of dogs and horses they insist on having the best sires which money or favour can secure, but they keep their wives under lock and key, demanding that they have children by none but themselves, even though they be foolish, or infirm, or diseased;