The Jews’ idea that ‘Uzayr is “a son of Allaah”
Question

                What does this beginning part of Surah Taubah 9:30 refer to? 
"The Jews call 'Uzair (Ezra) a son of Allah..."
Please answer as thoroughly as possible and feel free to provide references to more detailed and extensive discussions of this matter (Arabic langu
Praise be to Allah.When Allaah issued the command 
          to fight the Jews and Christians, in the aayah (interpretation of the 
          meaning):
“Fight 
          against those who (1) believe not in Allaah, (2) nor in the Last Day, 
          (3) nor forbid that which has been forbidden by Allaah and His Messenger  
          (Muhammad), (4) and those who acknowledge not the religion of truth 
          (i.e. Islam) among the people of the Scripture (Jews and Christians), 
          until they pay the Jizyah with willing submission, and feel themselves 
          subdued” (al-Tawbah 9:29)
-- 
          He then stated the reason that made it obligatory to fight them, which 
          was their disbelief in Allaah and their shirk – which included their 
          speaking ill of Allaah by attributing a son to Him, when He is the One, 
          the Self-Sufficient Master, He begets not, nor was He begotten, and 
          there is none co-equal or comparable unto Him. The Jews said that ‘Uzayr 
          is a son of Allaah, and the Christians said that the Messiah was a son 
          of Allaah. ‘Uzayr was a righteous man from among the Children of Israel, 
          who was venerated by the Jews. It was said that the reason why he was 
          venerated was that he had memorized the Tawraat (Torah), so the Jews, 
          or some of them, exaggerated about him and claimed that he was a son 
          of Allaah. So Allaah condemned them for that and told them that by saying 
          this they were doing the same as the mushrikeen who said that the angels 
          were daughters of Allaah. The Christians also spoke ill of Allaah when 
          they said that the Messiah was a son of Allaah; by doing so they resembled 
          the Jews and mushrikeen. Allaah says (interpretation of the meaning): 
        
“And 
          the Jews say: ‘Uzair (Ezra) is the son of Allaah, and the Christians 
          say: Messiah is the son of Allaah. That is their saying with their mouths, 
          resembling the saying of those who disbelieved aforetime. Allaah’s Curse 
          be on them, how they are deluded away from the truth!” [al-Tawbah 9:30] 
          
 See 
          Tafseer Ibn Katheer, the 
          second part of his tafseer of Soorat 
          al-Tawbah; Tafseer Ibn 
          Jareer; Tafseer al-Qurtubi.