Sayyiduna Wathilah bin al-Asqa' (may Allah be pleased with him) narrates that the Prophet (peace and blessings be upon him) said: "I was commanded to use the miswak until I feared that it would be made obligatory upon me."
Ahmad and al-Tabarani (in al-Mu'jam al-Kabir) recorded it; its chain contains a narrator, Layth bin Abi Sulaym, who is thiqah (trustworthy) but a mudallis (one who conceals his source), and he narrated it with 'an'anah (using "from").
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 2559