Because Imām Mālik Ibn Anas narrates from Ibn Shihab al-Zuhrī via Ḥanẓalah ibn ‘Alī from Abū Hurayrah from the Prophet (ṣallallāhu ‘alayhi wasallam) who said, “I swear by (Allah) the one who holds my soul in his hand! ‘Īsā (‘alayhissalām) will call the Talbiyah for Ḥajj at Fajj al-Rawḥā (around 30 miles from Madina)’."
(The Muwatta Imam Malik from the Transmission of Abdullah ibn Wahb, Abdurrahman ibn al-Qasim al-Utaqi, and Ma'n ibn Isa, and Abdullah ibn Maslamah al-Qa'nabi's al-Maliki (Bukhari's teachers) transmission, Musnad Ahmad, Bayhaqi in Shuab al-Iman, Sunan al-Kubra, Kanz al-Ummal, Sahih Muslim, Musnad al-Humaidi, Tafsir al-Qurtubi al-Maliki)
Imam Malik ibn Anas comments on this hadith and says, "Isa (AS) will either call out for Hajj or Umrah or both or he will perform Al-Hajj al-Qarin or do Umrah after his hajj once."
(Al-Bayan wa-Tahsil, V18, Pg. 28)
and, Imam Abdurrahman ibn al-Qasim al-Utaqi said, I heard Imam Malik ibn Anas say, "Whilst people will be in a city, they will hear the Iqamah to prayer and they will intend to start salah until suddenly a cloud will cover them, suddenly then Isa ibn Maryam (AS) will descend." Imam Muhammad ibn Rushd the Grandfather said, "Allah has surely informed us in his book from which falsehood does not appear from its front nor from behind it, that Isa ibn Maryam was not killed nor crucified and that Allah raised him up.”
(Al-Bayan wa-Tahsil, V18, Pg.37)
Furthermore, Imam Ibn Wahb (direct student of Imam Malik ibn Anas) and Ibn Habib (student of Imam Abdurrahman ibn al-Qasim al-Utaqi) both said, "The first of the signs of the day of judgement will be trials, then the dajjal, then the descent of Isa (AS)....." (The Commentary of Ibn Naji At-Tannukhi upon the Risalah of Ibn Abi Zayd al-Qayrawani)