"And that you will not be thirsty therein," meaning: you will not be thirsty. "Nor will you be exposed to the sun," meaning: the sun will not strike you.
Muhammad said: It is said: A man is exposed (dahaya) and is being exposed (yadha); this occurs when he emerges into the mid-morning sun (duha), which is the heat of the sun.
﴿وَأَنَّك لَا تظمأ فِيهَا﴾ أَيْ: لَا تَعْطَشُ ﴿وَلا تَضْحَى﴾ أَيْ: لَا تُصِيبُكَ شَمْسٌ.
قَالَ مُحَمَّدٌ: يُقَالُ: ضَحِيَ الرَّجُلُ يَضْحَى؛ إِذَا بَرَزَ إِلَى الضُّحَى، وَهُوَ حر الشَّمْس.
