All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.
It is permissible to see the circus if it is free from Islamic prohibitions as, in principle, all things are permissible. However, as far as we know, the circus is seldom free from Islamic prohibitions that require saying that it is forbidden.
Usually some magicians do magic tricks to attract the attention of the audience whereas it is not permissible to see magic and attend the places where magic is practiced. Indeed, Allaah, while describing the servants of the Most Merciful, says (what means): {And [they are] those who do not testify to falsehood, and when they pass near ill speech, they pass by with dignity.} [Quran 25:72]
Verily, magic is the greatest falsehood, and it is disbelief in Allaah, so it is neither permissible to see it nor to attend the places where it takes place. For more benefit, please to fatwa 255790.
Also, women who are scantily dressed may be present in the circus, either in the audience, where the place is mixed or in the members of the circus, where women perform some acrobatic acts or sports while wearing tight clothes that describe the shape of their bodies and their ‘awrah (parts of the body that must be covered in Islam).
Also, they incite animals to fight each other ; Ibn ‘Abbaas said, “The Prophet forbade inciting animals to fight each other.” [At-Tirmithi] An-Nawawi classified this hadeeth as saheeh (sound), while other scholars classified it as weak. Inciting animals to fight causes them pain and exhausts them without any benefit, while Islam advocates being kind with animals and taking care of them; please refer to fatwa 83830.
In addition to the above, there is a music band in the circus that plays throughout the show to help maintain the performance of movements at a particular time or to signal the end of a particular show and so forth while musical instruments are prohibited as underlined in fatwa 81545.
Moreover, the time of the circus show could be prolonged and this could lead to losing the time of the prayer or other Islamic obligations.
Verily, it is not permissible for a Muslim to attend places where evil takes place except for a correct purpose, like objecting to doing that evil. Allaah says (what means): {And when you see those who engage in [offensive] discourse concerning Our verses, then turn away from them until they enter into another conversation. And if Satan should cause you to forget, then do not remain after the reminder with the wrongdoing people.} [Quran 6:68]
Finally, a Muslim should preserve his time and not waste it in what is not beneficial. Allaah says in describing the believers (what means): {And they who turn away from ill speech.} [Quran 23:3] Ibn Katheer said while interpreting the above verse, "i.e. turning away from falsehood, which includes polytheism and sins and words and deeds that are of no benefit."
Allaah Knows best.