Muhammad bin Ishaq came to Imam Sajjad (a.s.) and complained about flood in the river in his town, which destroyed his property worth 500000 dirhams every year.
The Imam gave him a finger ring to throw into the river.
The narrator says: When I did that the flow of water smoothened and did not change in winter or summer.
Ithbatul Huda
Isbaatul Wilayah (Part One) – Ayatullah AliNamazi Shahroodi (r.a.)