Musannaf Ibn Abi Shayba 3:5021

Waki’ narrated to us, he said: Sufyan narrated to us, from ‘Amr ibn Qays al-Mula’i, from Salamah ibn Kuhayl, from ‘Amarah ibn ‘Umayr, he said: ‘Abdullah said: The most worthy of what we strive toward is the prayer.