Shaqiq bin Salamah (may Allah have mercy on him) says: I saw Sayyiduna Uthman bin Affan (may Allah be pleased with him) performing ablution. Then he mentioned the complete hadith; he says: When he washed his face, he passed (his fingers) through his beard three times and said: "I saw the Messenger of Allah (peace and blessings be upon him) doing just as you have seen me doing."
(b) Muhammad bin Isma'il al-Bukhari (may Allah have mercy on him) was asked about this hadith and said: It is hasan (good). And he said: In my view, the hadith of Uthman (may Allah be pleased with him) is the most authentic report regarding passing (the fingers) through the beard.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 246
It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him) that when the Messenger of Allah (peace and blessings be upon him) performed ablution, he would take water in his palm, put it under his chin, then pass it through his beard, and say: "This is how my Lord has commanded me."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 247
It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him): I brought water for ablution for the Messenger of Allah (peace and blessings be upon him), and he passed his fingers through his beard and the hair below his lower lip, and said: "This is how my Lord has commanded me."
(b) Regarding passing the fingers through the beard, marfu' narrations have been reported from Sayyiduna Ammar bin Yasir (may Allah be pleased with him), Sayyidah Aishah al-Siddiqah (may Allah be pleased with her) and Sayyidah Umm Salamah (may Allah be pleased with her); likewise from Sayyiduna Ali (may Allah be pleased with him). Then not doing so has been reported from Sayyiduna Ibn Umar (may Allah be pleased with them both), Hasan bin Ali (may Allah be pleased with them both), Imam al-Nakha'i (may Allah have mercy on him) and a group of the Successors.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 248