《资治通鉴·梁纪·梁纪六》
源子雍暗中派人给统万城送信，命令城中军民努力固守。
子雍潜遣人赍书，敕城中努力固守。
Yuan Zi-yong secretly sent someone to deliver a message to Tongwan City, ordering the soldiers and civilians of the city to do their utmost to defend it.