(a) It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "Had I not considered it a hardship for my Ummah, I would have ordered them to delay the Isha prayer and to use the siwak for every prayer."
(c) It is narrated from Malik (may Allah have mercy on him) that he (peace and blessings be upon him) said: "I would have ordered them to use the siwak with every prayer."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 154