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 delay the Isha prayer and to use the miswak with every prayer."
(b) Imam al-Shafi'i (may Allah have mercy on him) says: In this hadith there is evidence that the miswak is not obligatory but optional; had it been obligatory, he (peace and blessings be upon him) would have commanded the Companions (to use the miswak) even if it caused them hardship.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 145
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
Imam Malik bin Anas (may Allah have mercy on him) narrated this narration as marfu' (attributed to the Prophet).
(b) Imam al-Shafi'i (may Allah have mercy on him) mentioned it as marfu' in the narration of Harmalah, and Imam Malik (may Allah have mercy on him) narrated it in the Muwatta with (this) chain as mawquf (not attributed to the Prophet), and it does not mention ablution.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 147
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 made the miswak obligatory upon them with every ablution, and I would have delayed the Isha prayer until the middle of the night."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 148
It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that he (peace and blessings be upon him) said: "Were it not that I would be placing hardship on my Ummah", I think he (peace and blessings be upon him) said, "I would have commanded them to use the miswak with every ablution, and to delay the Isha prayer until a third of the night or half of the night."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 149
Sayyiduna Abu Hurayrah (may Allah be pleased with him) said: I heard the Prophet (peace and blessings be upon him) say: "If I did not dislike causing hardship to my Ummah," and the rest of the hadith was narrated like the previous hadith.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 150
It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "I see you coming to me in a state where there is grime on your teeth. Had I not considered it a hardship for my Ummah, I would have made the siwak obligatory upon them just as ablution has been made obligatory upon them."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 151
Sayyiduna Ibn Abbas (may Allah be pleased with them both) narrates from the Prophet (peace and blessings be upon him): "You come to me with grimy teeth; use the siwak."
There is disagreement about the chain of this hadith.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 152
It is narrated from Sayyidah Aishah (may Allah be pleased with her) that the Messenger of Allah (peace and blessings be upon him) said: "Ten things are part of the fitrah (natural disposition): trimming the moustache, letting the beard grow, using the siwak, sniffing water into the nose and blowing it out, clipping the nails, washing the finger joints, plucking the armpit hair, shaving the pubic hair, and pouring water (for cleaning)." Mus'ab said: I forgot the tenth, (it may be that) it is rinsing the mouth.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 153