All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.
This hadeeth is not authentic. Al-Kittaani mentioned it in his book entitled Tanzeeh Ash-Sharee’ah Al-Marfoo’ah ‘an Al-Akhbaar Ash-Shanee’ah Al-Mawdhoo’ah, and he stated that Al-Khateeb narrated it in Ruwaat Maalik from Is-haaq ibn As-Salt, and he said, “I did not narrate it from Maalik except with this chain of narrators.”
Also, Ath-Thahabi said in Al-Meezaan, “Is-haaq ibn As-Salt narrated a very objectionable hadeeth from Imaam Maalik [i.e. it was not reported by Maalik], and its chain of narrators is objectionable.”
The origin of the story was narrated by Imaam Muslim in his Saheeh, but the statement of Jaabir that you mentioned in the question: “I then thought in my head, if only Allaah informed me about his () waste, so that I may consume it! I saw that the earth on which he sat was clean. So I asked, ‘Did you not relieve yourself?’ to which he replied, ‘Yes, but the earth is ordered to hide away the excess of us Prophets’…” is not included in the wording of Imaam Muslim.
Allaah knows best.