《资治通鉴·晋纪·晋纪三十八》
正赶上姚兴因为西北地区的叛乱层出不穷，打算派一名重要的将领到那里镇抚，所以陇东太守郭播便请求派姚弼去镇守。姚兴并不听从，任命太常索棱为太尉、兼陇西内史，让他去招扶西秦。
会兴以西北多叛乱，欲命重将镇抚之；陇东太守郭播请使弼出镇，兴不从，以太常索稜为太尉、领陇西内史，使招抚西秦。
Just at that time, because of the frequent rebellions in the northwest, Yao Xing planned to send an important general there to pacify the area, thus, the Grand Prefect of Longdong Guo Bo requested that Yao Bi be sent to garrison the area. Yao Xing would not listen and appointed the Grand Master of Ceremonies Suo Leng as Grand Tutor and also Grand Minister of Longxi, so that he might go and appease Western Qin.