Abu al-Janub narrates: I saw Sayyiduna Ali (may Allah be pleased with him) taking water for ablution, so I hurried towards him to help him perform ablution. He said: O Abu al-Janub! Stop! Once I saw Sayyiduna Umar (may Allah be pleased with him) taking water for ablution, and I came forward to help him perform ablution, and he said: O Abu al-Hasan! Stop! (He told me:) Once I saw the Prophet (peace and blessings be upon him) about to perform ablution, and I came forward to help him perform ablution, and he (peace and blessings be upon him) said: "O Umar! Stop! I dislike that anyone should share with me in my ablution."
Imam Abu Ya'la and Imam al-Bazzar recorded this report, and Abu al-Janub is da'if (weak).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الطهارة / 1147
Sayyiduna Abu Ayyub (may Allah be pleased with him) narrates: Once I went out with the Prophet (peace and blessings be upon him) when the sun had set, or was about to set, and I had a vessel of water with me. The Prophet (peace and blessings be upon him) went to relieve himself, and I kept waiting for him until he (peace and blessings be upon him) came back, and I helped him (peace and blessings be upon him) perform ablution. The narrator then mentioned the complete hadith.
Imam al-Tabarani recorded this report in al-Mu'jam al-Kabir; its chain contains a narrator, Abd al-Aziz bin Aban, on whose weakness the hadith scholars are agreed.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الطهارة / 1148