It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "Make the use of the miswak obligatory upon yourselves, for it is a means of purification for the mouth and a cause of Allah's pleasure."
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 5865
Hadith Gradingحکم دارالسلام:صحيح لغيره، وهذا إسناد ضعيف لضعف ابن لهيعة.