One of Rasul Allah's wife, Umm Al-Mumineen Safiyyah bint Huyayy (radi'Allahu anha) was the daughter of one of the Jewish leaders of Madinah. When she had first felt the rays of Islam enter her blessed heart, she accepted Islam, and then related to the Prophet - sal Allahu alayhi wa sallam what she encountered....
It was the day that Anas (radi Allahu anhu) describes as the most radiant day to every come upon al-Madinah, i.e. the day Rasul Allah salAllahu alayhi wa sallam entered it. All the Ansar men, women and children gathered to greet him, cheers of praise to Allah filled the air. Amongst the gathering were 2 men; as much as the Ansar and Muhaajireen revered the Prophet, they despised him. It was the father of Safiyyah (radi Allahu anha) and her uncle. She was only a youngster as she looked into the darkness and gloom that had enveloped their faces when they returned home that day.
Her Jewish uncle asked, "Is it him? Is it the Prophet that our scriptures speak of?"
Huyayy lowered his head and said, "Yes. It is him."
"Then what shall we do?" Safiyyah's uncle continued.
Huyayy looked into his eyes and said, "Till the final day we shall be his bitterest enemies!"
From the very first rakaah of Taraweeh we read the verse in the opening Surah (Al-Fatihah):
"Guide us to the straight path - The path of those upon whom You have bestowed favor, not of those who have evoked (Your) anger!.."
Adiyy ibn Hatim asked Rasul Allah salAllahu alayhi wa sallam,
"who it was that evoked Allah's anger?"
Muhammad said, "It was the Jews"
(Tafseer Ibn Katheer)
The Jews were cursed because
1) They followed only what they wanted to
2) They changed the words of Allah
3) They claimed that they are the beloved children of God
4) They made blaphemous statements
5) They murdered the prophets sent to them
Allah commands us in the Quran:
"O you who have believed, do not take the Jews and the Christians as allies. They are allies of one another. And whoever is an ally to them among you - then indeed, he is one of them. Indeed Allah does not guide the wrongdoing people." - Maaidah 5/51