Musannaf Ibn Abi Shayba 3:2990

Hushaym ibn Bashir narrated to us, he said: Yunus ibn Ubayd narrated to us, from Humayd ibn Hilal, from Imran ibn Husayn, that he used to pray two rak'ahs after Jumu'ah. It was said to him, "O Abu Nujayd, what are the people saying?" He said, "And what are they saying?" He said, "They say that you pray two rak'ahs [connected] to the Jumu'ah, so they become four." Imran said, "For the ribs of my chest to be broken is more beloved to me than that I should do that." When the following Jumu'ah came, he prayed the Jumu'ah, then he sat with his knees drawn up (ihtaba), and he did not pray anything until the prayer of Asr was established.