Sayyiduna Ibn Umar (may Allah be pleased with them both) narrates that the Prophet (peace and blessings be upon him) said: "I saw myself (in a dream) using the siwak, and then two men came to me, one of them older than the other. I handed the siwak to the younger of the two, and it was said to me: 'Give it to the elder.' So I gave it to the elder."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 171
Sayyiduna Ibn Umar (may Allah be pleased with them both) said: I saw the Messenger of Allah (peace and blessings be upon him) using the siwak; then he (peace and blessings be upon him) gave it to the eldest of the people and said: "Jibril (peace be upon him) ordered me to give the siwak to the elder."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 172