"Whoever tells you that the Messenger of Allah ﷺ urinated while standing, do not believe him. The Messenger of Allah never urinated standing from the time the Quran was revealed to him."
من حدثك أن رسول الله ﷺ بال قائما فلا تصدقه، ما بال رسول الله قائما منذ أنزل عليه القرآن.
Ahmad (25045), Hakim (1/181), and Bayhaqi (1/101) all narrated it through a chain going back to Sufyan Thawri, from Miqdam bin Shurayh, from his father, from Ayesha who said, then she mentioned it.Miqdam bin Shurayh is the son of Hani Harithi Kufi. Ahmad, Abu Hatim, and Nasai all considered him reliable. Shurayh bin Hani is the son of Yazid Harithi Kufi. Ibn Main, Nasai, and others considered him reliable. Its chain of transmission is sahih, and it does not fall below the level of Bukhari's chains in soundness, even though Miqdam and his father are not among the narrators Bukhari relied on. Bukhari never committed himself to including everything that is sahih, so he should not be faulted for that.Sheikh Islam bin Taymiya said, "There is no book among the books of prophetic tradition more beneficial than Sahih Bukhari, but it alone does not establish the foundations of knowledge, nor does it fulfill the complete purpose sought by someone who wishes to master the branches of knowledge, since one must also become acquainted with other hadiths." Majmu Fatawa (10/665).The hadith of Ayesha was also narrated by Tirmidhi (12), Nasai (29), and Ibn Majah (307), all through a chain going back to Sharik, from Miqdam bin Shurayh, from his father, from Ayesha, who said, "Whoever tells you that the Prophet ﷺ used to urinate standing, do not believe him. He never urinated except sitting down."In its chain of transmission is Sharik, who is the son of Abdullah Nakhai, the judge of Kufa. Ibn Main said of him, "He is reliable but makes mistakes." Yaqub bin Sufyan said, "He is reliable but has a poor memory," though he was corroborated by another narrator.Tirmidhi said, "The hadith of Ayesha is the best and most sahih thing on this subject." However he did not rule it sahih or hasan outright, he only said it was "the best and most sahih thing on this subject" in comparison to the hadith of Umar, who said, "The Prophet ﷺ saw me urinating standing, so he said, 'O Umar, do not urinate standing.' From then on, I never urinated standing again."Tirmidhi said, "This hadith was only raised to the status of a Prophetic saying by Abdul-Kareem bin Abu Mukhariq, who is considered daif among the people of hadith. Ayub Sakhtiyani declared him daif and criticized him." End of quote.I say, this hadith of Umar was also recorded by Ibn Majah (1/112) through the chain of Abdul-Kareem bin Abu Mukhariq, except that he said, "Abdul-Kareem bin Abu Umaya," but the correct version is that Abu Umaya was the kunya of Abdul-Kareem.Busiri said in Zawaid, "There is consensus that Abdul-Kareem is daif, and he alone transmitted this report."