It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Were it not that I would be placing hardship on my Ummah, I would have commanded them to use the miswak with every ablution."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 146