• I heard Ishaq ibn Ibrahim say: "The Sunnah from the Prophet, peace and blessings of Allah be upon him, has passed regarding the encouragement to perfect (isbag) wudu' and to comb the fingers. The Companions of Muhammad and those who followed them said the same, such that they would move their rings during wudu' and remove them until the water reached the area of the rings. Whatever resembles that, such as strings or threads on the fingers, is treated likewise."
He said: "Sometimes a man uses a thread on his fingers to remember something. When he performs wudu', he exerts effort to remove it until the water reaches it. In what the Prophet, peace and blessings of Allah be upon him, and his Companions established regarding the combing of the fingers of the hands and feet, there is evidence for this as well, and it is the most similar thing to it. Therefore, no one performing wudu' or performing ghusl (full body wash) due to janabah (major ritual impurity) should neglect that, and the same applies to women during their menstruation, janabah, or wudu'."
"As for what those people said—that it suffices him not to move it, whether it is tight or loose, provided it is his strongest assumption that he has conveyed the water to it—that is a mistake and a lack of caution in wudu'. What has passed from the Prophet, peace and blessings of Allah be upon him, regarding its movement is evidence for it: his encouragement to perfect wudu', and his statement after finishing the prayer in which he felt doubtful, he said: 'What is the matter with me that I do not wash the space between the nail and the fingertip of one of you?' and his statement: 'Woe to the heels from the Fire.' Thus, the sites of rings, threads, and fingers are places of obligatory wudu', so it is incumbent upon him to track them just as he tracks the heel and combs the fingers. If he does not move his ring during his wudu', or the thread he ties around his finger, and he knows that the water has reached [the skin], it suffices him, if Allah wills. But if it is only an assumption, he must wash its place."
199 - 'Abd al-Rahman ibn al-Mubarak narrated to us, he said: Muhammad ibn Ya'la narrated to us, from Salim ibn 'Abd al-A'la, from Nafi', from Ibn 'Umar, that the Prophet, peace and blessings of Allah be upon him, used to fasten a thread around his finger to remember a need by it.
