Narrated Mujahid:
Ibn `Abbas said, "Allah ordered His Prophet to celebrate Allah's praises after all prayers." He refers to His Statement: 'After the prayers.' (50.40) (ES)
USC-MSA web (English) reference: Vol. 6, Book 60, Hadith 375 (ES)
Arabic reference (ES): Book 65, Hadith 4852 (ES)