《新唐书·列传·卷一百四十六》
皇帝又命乘胜劝降。赤辞的侄子思头暗中送来降书，其下属拓拔细豆也降。
帝因其胜又令约降，赤辞从子思头潜纳款，其下拓拔细豆亦降。
The emperor once again ordered Sheng to take advantage of his victory and encourage the enemy to surrender. Chidi’s nephew, Situ, secretly sent a letter of surrender, and his subordinate, Tuoba Xidou, also surrendered.