Ibn Ma'dan (may Allah have mercy on him) narrates from one of the Companions (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) saw a man praying, and on his foot was a patch the size of a dirham that water had not reached. So the Prophet (peace and blessings be upon him) ordered him "to repeat the ablution and the prayer."
(b) It is like this in the mursal narration, and also in a connected (mawsul) one.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 392
Sayyiduna Anas (may Allah be pleased with him) relates that a man came to the Prophet (peace and blessings be upon him). He had performed ablution and left a spot the size of a fingernail dry on his foot. the Messenger of Allah (peace and blessings be upon him) said: "Go back and perform your ablution well."
(b) Imam Abu Dawud (may Allah have mercy on him) says that this hadith is not well known, and only Ibn Wahb narrated it from Jarir bin Hazim.
(c) Imam Abu Dawud (may Allah have mercy on him) says: Al-Hasan (al-Basri) narrated it from the Prophet (peace and blessings be upon him) with the meaning of Qatadah's hadith, and this is mursal.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 393
Something similar is reported from Sayyiduna Umar (may Allah be pleased with him), that he (peace and blessings be upon him) said: "Go back and perform your ablution well." So he went back, then prayed.
(b) The Shaykh says that Ma'qil narrated it like the previous hadith.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 394
Sayyiduna Jabir (may Allah be pleased with him) says that Umar bin al-Khattab (may Allah be pleased with him) saw a man performing ablution, and a spot on his foot remained dry. Sayyiduna Umar (may Allah be pleased with him) said: Repeat the ablution.
(b) It is narrated from Hadrat Umar (may Allah be pleased with him) that the order he gave to repeat the ablution was recommended, and only washing the foot was obligatory.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 395
Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) saw a man on whose foot there was a spot that water had not reached. He (may Allah be pleased with him) said: Will you attend the prayer with this ablution? He said: O Commander of the Believers, the cold is severe, and I have nothing to protect me from it. He (may Allah be pleased with him) softened towards him after he had been about to punish him, and said: Wash the part of your foot that you left, and repeat the prayer. And he ordered that a woollen garment be given to him.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 396
(a) It is narrated from Nafi' that Ibn Umar (may Allah be pleased with them both) performed ablution in the market, washing his hands, face and forearms three times each. Then he entered the mosque and wiped over his leather socks after his ablution had dried, then prayed.
(b) This narration is authentic; its narrator is Ibn Umar (may Allah be pleased with them both), and it is well known from Qutaybah with these words.
(c) Ata, the Successor (may Allah have mercy on him), saw no harm in performing the ablution with breaks between the parts. This is also the view of al-Hasan (may Allah have mercy on him) and al-Nakha'i (may Allah have mercy on him), and it is the more correct of Imam al-Shafi'i's (may Allah have mercy on him) two views.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 397
It is narrated from Sayyiduna Abu Umamah or his brother (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) saw some people on whose heels a spot the size of a dirham or a fingernail had not been reached by water, and he (peace and blessings be upon him) said: "Woe to the heels from the Fire." The narrator says that each one of them would look at his heels, and if water had not reached them, he would repeat his ablution.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 398