Ibn Rajab has a section in ‘Lata’if al-Ma’arif’ (p. 272-273) about the virtues of fasting during hot days. Since Ramadan will start in the summer this year, this will be a good encouragement:
“…And from the acts of worship whose reward is multiplied during the heat is fasting, and this is because of the thirst that one experiences in the mid-day heat.
This is why Mu’adh bin Jabal expressed regret on his deathbed that he would no longer experience this mid-day thirst, as did other early Muslims.
And it was related that Abu Bakr would fast in the summer and not fast in the winter, and ‘Umar advised his son ‘Abdullah on his deathbed: “Try to obtain the characteristics of faith,” and the first one he mentioned was fasting in the intense summer heat.
And al-Qasim bin Muhammad said that ‘A’ishah would fast in the intense heat, and he was asked: “What drove her to do this?” He replied: “She would take advantage of the days before death.” And some of the righteous women would choose the hottest days and fast them, saying: “If the price is low, everyone will buy,” meaning that she wanted to do those actions that only a few were capable of due to how hard it was to do them, and this is indicative of the high aspirations these women had.