Musannaf Ibn Abi Shayba 35:36

Waki’ narrated to us, from Ibn Abi Khalid, from al-Sha’bi, regarding a man who disavows what is in his wife’s womb: He said, "He performs *li’an* (imprecation) with her." And he mentioned that Abu Hanifa did not consider *li’an* to be applicable in the case of pregnancy.