Musannaf Ibn Abi Shayba 37:191

Yazid ibn Harun narrated to us, he said: Muslim ibn Sa'id informed us, from Mansur ibn Zadhan, from Mu'awiyah ibn Qurrah, from Ma'qil ibn Yasar, he said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Worship during the time of tribulation (fitnah) is like emigration (hijrah) to me."