The Battle of Samara Bend or the Battle of Kernek was the first battle between Volga Bulgaria and the Mongols, probably one of the first major battles the Mongols lost. It took place in autumn 1223, at the southern border of Volga Bulgaria. The Bolghars allegedly retreated and the Mongols pursued them. Then the main Bolghar forces ambushed the Mongols. After Mongols were rounded up, the Bolghar massacred them and only 4,000 managed to escape, according to local oral traditions.
However, it is worthy to note that in Chinese source that there is no record of the defeat. Both the paragraphs about Subutai and Jebe has not even mentioned the battle. Also, on the return of Subutai, the Khan's attitude towards him didn't indicate any hint of defeat. The Chinese resource did record, however, Batu Khan's grudge against Subutai, for Subutai's late show up in the battle of Sajo, causing his lieutenant's death. It is somewhat unlikely that the Chinese source would record Batu's grudge in the overall successful Hungary campaign, but not a total defeat of Subutai.