Uthman bin Muhammad · The Book of Purification and its Sunnah

"If anyone tells you that the Messenger of Allah urinated while standing, do not believe him, for I (always) saw him urinating while sitting down."

"The Messenger of Allah said: 'Most of the torment of the grave is because of urine.'"

The Prophet was asked about seawater, and he said: "Its water is a means of purification, and its dead meat is permissible." (Hasan) Another chain with similar wording.

"The Messenger of Allah used to perform ablution washing each part three times."