Musnad Abu Ya'la al-Mawsili 154:120

5750. Khalaf ibn Hisham al-Bazzar narrated to us, Abu 'Awanah narrated to us, from Simak ibn Harb, from Mus'ab ibn Sa'd, who said: Ibn Umar entered upon Abdullah ibn Amir to visit him (during his illness), and he (Ibn Amir) said, "What prevents you from supplicating for me?" He (Ibn Umar) said, "I heard the Prophet, may Allah bless him and grant him peace, say: 'Indeed, Allah does not accept a prayer without purification.'"