Which Qur'anic verse makes the five prayers obligatory, in reply to those who say nothing in the Qur'an requires five prayers?

Muslims have unanimously agreed that Allah has ordained five prayers day and night, and this is a matter known by necessity of the religion; whoever denies it is a disbeliever. The Holy Quran has indicated the times of the five prayers in His saying, the Almighty: "Establish prayer at the decline of the sun until the darkness of the night, and [recite] the Quran of dawn. Indeed, the recitation of dawn is ever witnessed." (Al-Isra: 78). So, "the decline of the sun" includes the Dhuhr and Asr prayers, "the darkness of the night" includes the Maghrib and Isha prayers, and "the Quran of dawn" means the Fajr prayer. A Muslim must choose a righteous friend who helps him do good and beware of befriending those who commit innovations.