I say, with Allah's guidance: It is recommended to delay the Dhuhr prayer in the summer and to hasten it in the winter. As narrated by Abu Huraira, Abu Dharr, and Abu Saeed, may Allah be pleased with them, the Prophet (peace be upon him) said: 'Cool down the prayer, for the severity of heat is from the breath of Hell.' This is found in Sahih al-Bukhari 3: 1189, Sahih Muslim 1: 430, and Sahih Ibn Khuzaymah 1: 170. And from Anas, may Allah be pleased with him: 'The Messenger of Allah (peace be upon him) would delay the prayer when it was hot, and hasten it when it was cold.' This is in Sunan an-Nasa'i al-Kubra 1: 465, and its narrators are trustworthy as mentioned in I'la al-Sunan 2: 35. See: Al-Wiqaya 1: 37, and Al-Kanz 1: 83, and Allah knows best.