It is narrated from the Mother of the Believers, Sayyidah Aishah (may Allah be pleased with her), that the Messenger of Allah (peace and blessings be upon him) said: "The miswak is a cause of purifying the mouth and a means of the Lord's pleasure."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 140