I say, and with God's success: It is not obligatory, but it is recommended to perform the washing for it; as narrated by Muslim in his Sahih from Ubaidullah bin Abdullah, may Allah be pleased with him, who said: "I entered upon Aisha and said to her: 'Will you not tell me about the illness of the Messenger of Allah, peace be upon him?' She said: 'Yes, the Prophet, peace be upon him, became very ill and said: 'Have the people prayed?' We said: 'No, they are waiting for you, O Messenger of Allah.' He said: 'Put water for me in the basin,' and we did so, and he washed. Then he went to stand, but he fainted, then he regained consciousness and said: 'Have the people prayed?' We said: 'No, they are waiting for you, O Messenger of Allah.' He said: 'Put water for me in the basin,' and we did so, and he washed..." And Allah knows best.