How do we reconcile that hardship is not rewarded if intended for its own sake, with the Hadith of the man who did not buy a donkey to be rewarded for the multitude of his steps to the mosque, and the Prophet, peace and blessings be upon him, approved of that?

The fundamentals of Islamic law are based on ease, where the Lawgiver does not intend hardship for its own sake in religious obligations, but rather the realization of the obligated person's benefit in this life and the hereafter. An obligation might entail hardship, such as Jihad, in which case the reward is amplified to encourage participation. Walking to the mosque is commendable, and every step is recorded as a good deed, and distance increases the reward due to the hardship, but hardship is not intended initially. The Hadith, "Banu Salimah, stay in your houses, your footsteps will be recorded," does not indicate an intention of hardship, but rather the Prophet's ﷺ dislike for Madinah to become vacant, along with seeking reward for the multitude of steps. Imam Al-Shatibi holds that the obligated person should not intend hardship for its own sake due to its great reward; rather, they should intend the action, which might have its reward amplified due to its great hardship. Therefore, intending hardship contradicts the intention of the Lawgiver and is invalid. The Lawgiver does not intend hardship itself through religious obligations, and the obligated person's intention of hardship for its own sake is invalid and contradictory to the Lawgiver's intention. The Hadiths that seemingly request hardship do not mean intending hardship for its own sake; rather, they indicate that the reward is amplified in proportion to the hardship of the worship, as in fasting on a hot day, and not intending to be severe with oneself. The Prophet ﷺ forbade being severe with oneself in worship, such as extreme asceticism (tabattul) and fasting while standing in the sun.

The predominant view is that walking to prayer and increasing steps to mosques is an act of worship intended in itself, just as Tawaf and Sa'i are intended acts of worship. This is supported by numerous Hadiths regarding the virtue of walking and increasing steps to mosques, and preferring the distant mosque. Hardship in these cases is secondary and not intended for its own sake; what is intended is the action whose difficulty increases.