In a previous post on this blog https://edwardwhite.mataroa.blog/blog/the-life-protecting-dharani-from-tongtian-xiao/ I mentioned a 'life protecting mantra' used in Chinese Buddhism: It is a mantra that is recited over water to ensure that the beings within it will get fortunate rebirths.
These mantras are found in two compilations of Vinaya, the 毗尼日用切要 https://cbetaonline.dila.edu.tw/zh/X60n1115_001 (Daily Essentials of the Vinaya) and 毗尼日用錄 https://cbetaonline.dila.edu.tw/zh/X1114 (A record of Daily Vinaya).
In the Daily Essentials of the Vinaya the mantra occurs thrice. The first entry is titled 飲水- Drinking water, and provides a short ritual for drinking water, which is as follows
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飲水- DRINKING WATER
佛觀一鉢水， 八萬四千蟲， 若不持此呪， 如食眾生肉。
The Buddha, in observing a bowl of water
Sees 84,000 creatures.
If this mantra is not recited
It is as if eating the meat of all beings
唵，嚩悉波囉摩尼，莎訶(三徧)。 OM WA XI BO LUO MO NI SO HE (recite thrice) ————————
This verse and mantra is found in the 毗尼日用錄 A record of Daily Vinaya, in an entry called 飲水偈呪 (A mantra for drinking water). The entry is identical with the above, except that it states the mantra is to be recited 7 times, and adds the following comment
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如先禮佛後而飲水更妙
If one pays respects to the Buddha and then drinks the water , it would be even more effective.
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The second ritual is part of a longer series of entries entitled 供淨瓶- Offering a Kalasha. The Kalasha, or to use the direct translation of its chinese name, Purifying Vase, is a vase of water that's offered daily to the buddhas.
The ritual begins by taking the vase from its position on the altar, and rinsing it thrice with clear water, taking care that the rising water is not thrown back into the water source. A mantra is recited as this is done. (蕩淨瓶真言。) After that, the vase is filled with clear water, and the above-mentoned mantra (唵，嚩悉鉢囉摩尼，莎訶) is silently recited thrice. The celebrant then goes to the altar and kneels. Holding the vase in his left hand and making a mudra with his right, he chants the great compassion mantra seven times before offering it. At the end of the day the water is scattered in a clean place as an offering to all sentient beings. This process is accompanied by more mudras, mantras and visualisations.
The last use of the mantra is a ritual called 'fetching water' 取水 The entry begins with a comment about the water filter used by monks, and meditations on water. It ends with the words
凡取水時，誦此諸佛德名偈呪，功德無涯，可謂真持戒者
。"Whoever fetches water, and chants the following names of the Buddhas, gatha and mantra, will have boundless merit, and may be called a true upholder of the precepts.
The ritual is as follows:
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若見流水，當願眾生
得善意欲，洗除惑垢。
When seeing flowing waters,
[I vow] “May all beings
acquire wholesome aspirations
and wash away delusion’s defilements.”
南無歡喜莊嚴王佛
I take refuge in Joyful Adornment King Buddha
南無寶髻如來
I take refuge in Precious Topknot Buddha
南無無量勝王佛
I take refuge in Unlimited Victorious King Buddha
唵，嚩悉波羅摩尼，莎婆訶(三徧)。 OM WA XI BO LUO MO NI SA PO HE (recite thrice)
若見大河， 當願眾生：
得預法流， 入佛智海。
When seeing a great river,
[I vow] “May all beings
be able to enter the stream of the Dharma
and flow into the Buddha’s ocean of wisdom.”
若見橋道， 當願眾生：
廣度一切， 猶如橋梁。
When seeing a road across a bridge,
[I vow]“May all beings
extensively liberate all beings,
thereby acting just like a bridge.”
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The mantra is written with a slight variation (the Svaha at the end is written with three syllables rather than 2). The Gathas are taken from the 11th chapter of the Flower Ornament Sutra (Avatamsaka Sutra). I have taken them from Bhikshu Dharmamitra's translation of the sutra, modifying them to make the speaker the person making the vow, as is implied by the context here.
Beyond these sources the author has been unable to find a sutra where this mantra came from.