Sayyiduna Uthman (may Allah be pleased with him) called for water and performed ablution. He poured water with his right hand onto his left hand, then washed them both up to the wrists. Then he rinsed his mouth and sniffed water into his nose three times, then he mentioned washing the limbs three times each in the ablution. Then he wiped his head and washed his feet. "I saw the Messenger of Allah (peace and blessings be upon him) performing ablution just as you have seen me performing ablution."
The Shaykh says: Washing the limbs in this way is sunnah or recommended, not obligatory. This is also the position of Ata, Ibn Sirin and the companions of Abdullah bin Mas'ud (may Allah be pleased with him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 214