Volume 3, Book 34, Number 426 :
Narrated by Ibn ‘Abbas (radiallaahu `anhu)
Once ‘Umar (radiallaahu `anhu) informed that a certain man sold alcohol. ‘Umar (radiallaahu `anhu) said, “May Allah curse him! Doesn’t he know that Allah’s Apostle (sallallaahu `alayhi wasallam) said, ‘May Allah curse the Jews, for Allah had forbidden them to eat the fat of animals but they melted it and sold it.”
Volume 3, Book 34, Number 427 :
Narrated by Abu Huraira (radiallaahu `anhu)
Allah’s Apostle (sallallaahu `alayhi wasallam) said, “May Allah curse the Jews, because Allah made fat illegal for them but they sold it and ate its price. “
We studied previously that when Allah forbids a thing, He forbids its price. Animal fat was haraam for the Jews. To have a way around it, they used to sell it to others and consume its price. This is wrong because of the rule mentioned in the beginning. Similarly, alcohol is forbidden for Muslims and so is its price. We can’t drink it OR sell it to non-Muslims. Its price is forbidden too.
Here’s an article about Jews written by Muhammad Alshareef explaining briefly the reasons Allah cursed them in the Quran.
Hadith no. 209 is a repeat. Read it here.
Narrated Ibn ‘Abbas:
Allah’s Apostle drank milk, rinsed his mouth and said, “It has fat.”
We all know that, right? But there’s another point to it. Prophet (SAW) is giving the reason for rinsing his mouth. It has fat. Get it?
So, the sunnah to be derived is: rinse your mouth before praying if you’ve eaten a fat-containing food. :)