 Also around this time, Ashina Duojishi's brother and successor, the Chuluo Khan Ashina Qilifu planned a major assault on Tang, and as part of the plan, he requested Dou to cross the Taihang Mountains and meet him at Jin (晉州, roughly modern Linfen, Shanxi) and Jiang (絳州, roughly modern Yuncheng, Shanxi) Prefectures, but Ashina Qilifu soon died and did not carry out the campaign.At the same time, Dou also executed Song, who often gave Dou honest and valid criticism, after false accusations, and it was said that thereafter no one dared to criticise Dou further, and that Dou's governance began to suffer because of it.In spring 621, Dou defeated Meng Haigong and captured him, keeping him as a general.