I say, and with God's success: The obligatory prayer, the prostration of recitation, and the funeral prayer are not valid when the sun is at its zenith until it sets. However, voluntary prayers during this time are valid but are strongly disliked; as narrated by Uqbah ibn Amir Al-Juhani, may Allah be pleased with him, who said: "There are three times when the Messenger of Allah, peace be upon him, forbade us to pray or to bury our dead: when the sun rises until it is fully risen, when the sun is at its zenith until it tilts, and when the sun is about to set until it sets," in Sahih Muslim 1: 568, Musnad Al-Mustakhraj 2: 424, Sahih Ibn Hibban 3: 348, Sunan Al-Tirmidhi 3: 348, and Sunan Abu Dawood 3: 208. And from Ibn Abbas, may Allah be pleased with both of them, who said: "Witnesses whom I trust testified to me, and the one I trust most is Umar, that the Prophet, peace be upon him, forbade praying after the dawn prayer until the sun rises and after the afternoon prayer until the sun sets," in Sahih Al-Bukhari 1: 211. See: Maraqi Al-Falah, pages 186-187, and Allah knows best.