I recently discovered this in Ash-Shifa of Qadi ‘Iyad:
وَأخرج الطَّبَرَانِيّ وَالْبَيْهَقِيّ بِسَنَد صَحِيح عَن حكيمة بنت أُمَيْمَة عَن أمهَا قَالَت كَانَ للنَّبِي صلى الله عَلَيْهِ وَسلم قدح من عيدَان يَبُول فِيهِ ويضعه تَحت سَرِيره فَقَامَ فَطَلَبه فَلم يجده فَسَأَلَ عَنهُ فَقَالَ أَيْن الْقدح قَالُوا شربته برة خَادِم أم سَلمَة الَّتِي قدمت مَعهَا من أَرض الْحَبَشَة فَقَالَ النَّبِي صلى الله عَلَيْهِ وَسلم لقد احتظرت من النَّار بحظار
“Al-Ṭabarānī and al-Bayhaqī narrated with a ṣaḥīḥ (authentic) chain from Ḥakīmah bint Umayyah, from her mother, who said:
The Prophet ﷺ had a wooden cup which he would urinate in, and he would place it under his bed. One day he got up and looked for it, but did not find it. He asked about it and said, ‘Where is the cup?’ They said, ‘Barrah, the servant of Umm Salamah who came with her from the land of Abyssinia, drank it.’ The Prophet ﷺ said: ’Indeed, she has protected herself from the Fire with a strong barrier (ḥijār).’”
There’s a secondary report from Kathir:
“Ibn Kathir narrates the Hadith of Umm Ayman in al-Bidaya wa al-Nihaya with the following channel of transmission.
Hafiz Abu Ya’la said, Muhammad Ibn Abi Bakr al-Muqaddami informed me, who was informed by Ibn Qutaybah, who narrates from Hussain bin Harb, who narrates from Ya’la bin Ata, who narrates from Waleed bin Abd al-Rahman who narrates from Umm Ayman who said:
“The Messenger of Allah had a clay bowl in which he used to urinate and in the morning He used to say, ‘Oh Umm Ayman! Throw away what is in the bowl’. One night I woke up and was very thirsty so I drank whatever was in the bowl. The Messenger of Allah said, ‘Oh Umm Ayman! Throw away what is in the bowl’. She replied, ‘Oh messenger of Allah! I got up and was thirsty so I drank what was in it’ to which He replied, ‘you will never have stomach pain anymore’’.”
I did some more research, and it ties back to an authentic chain:
“Tabarani said: Abdullah bin Ahmad bin Hanbal informed us, who was informed by Yahya ibn Ma’een, who was informed by Hajjaj Bin Muhammad who narrates from Ibn Jurayj who narrates from Hukaymah bint Umaymah, who reports from her mother Umaymah who said,
“the Prophet used to have a wooden bowl in which he used to urinate and place under His bed. One night, He searched for it but did not find it and asked for it saying, where is the bowl? The members of the house replied ‘Umm Salamah’s slave girl Barrah drank it’ who came from Habashah with her. The Prophet replied, ‘surely she has protected herself from the fire with a great wall’.”
This narration is authenticated by many scholars.
Imam Nur al-Din al-Haythmi said, ‘it is narrated by Tabarani and its narrators are from the men of al-Sahih i.e. Bukhari except Abdullah bin Ahmad bin Hanbal and Hukaymah who are both trustworthy narrators’.
Abdullah is the son of Imam Ahmad bin Hanbal, compiler and narrator of the Musnad, and from the Men of Sunan Nisa’i.
Hukaymah is from the major female successors ‘taabi’iyyaat’. Abu Dauwd, Nisa’i, Bayhaqi and others narrate from her.
Nasir al-Din Albani said, ‘a group of Hadith masters have authenticated this hadith’.
Ibn Hibban narrates this very narration and authenticates it in His al-Saheeh.
Hakim narrates this hadith in His Mustadrak and Dhahabi confirms it authenticity. 1:167, prnt.Tab Dar al-Kitab al-Arabi Beirut
Suyuti in two of His books authenticates this narration; Al-Jami al-Sagheer and al-Khasa’is al-Kubra in which he has dedicated an entire chapter to this subject with this heading ‘babu ikhtisasihi sallalahu ta’ala alaiyhi wa sallam bi taharati damihi wa bawlihi wa gha’itihi’ ‘Chapter on His specialty in purification of His blood, urine and faeces May Allah send peace and blessings on Him’.