《左传·桓公·桓公十六年》
《春秋》所以记载这件事，是由于不妨碍农时。当初，卫宣公和父亲的姬妾夷姜私通，生了急子。
书时也。初，卫宣公烝于夷姜，生急子，属诸右公子。
The reason why the Spring and Autumn Annals recorded this event is that it did not interfere with the farming season. Originally, Duke Xuan of Wei had an affair with his father's concubine, Lady Yi Jiang, and they gave birth to Ji Zi.