Volume 2, Book 23, Number 443:
Narrated Ibn Abbas:
The Prophet once passed by two graves, and those two persons (in the graves) were being tortured.
He said, “They are being tortured not for a great thing (to avoid). One of them never saved himself
from being soiled with his urine, while the other was going about with calumnies (to make enmity
between friends). He then took a green leaf of a date-palm tree split it into two pieces and fixed one
on each grave. The people said, “O Allah’s Apostle! Why have you done so?” He replied, “I hope that
their punishment may be lessened till they (the leaf) become dry.”