Musannaf Ibn Abi Shaybah

Hazrat Saeed bin Jubair says that if a person is praying while sitting cross-legged, then during bowing (ruku) and prostration (sajdah), he should bend his leg.

Hazrat Hisham says that Hazrat Ibn Sirin used to pray sitting cross-legged; when he would go into ruku, he would bend his leg.

Abu Hafs says that I saw Hazrat Anas that he performed prayer while sitting, and when he intended to bow (ruku‘), he would bend his leg.