I strongly believe that it is good to include the Arabic text with translations. The primary reason is that at the end of the day, especially in literary texts, any translation, no matter how faithful, is an interpretation. It is a subjective rendering of the meaning as you understand it. For those of your readers who are proficient in Arabic, not having access to the original may be frustrating.
I would also advise, especially since there are now so many hassle free ways of inputting Arabic script, to include the Arabic in Arabic script and not transliterate, where full sentence and longer quotations. For words or short phrases quoted inline transliteration is of course better.
If you are going to have many translations in your thesis, and most of them are your own translations, it may be worth making a note at the beginning (with the notes on transliteration, dating and referencing—after acknowledgments) that all translations are yours unless otherwise indicated.
In this section there are suggestions about the following,