It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "When you ask of Allah, ask Him with the palms of your hands, and do not ask Him with their backs, and wipe your faces with them."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10733