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