it is by mention of the Fire, mention of some of the kinds of punishment therein, mention of the conditions of the criminals, or the like.
His statement, “and asking at a verse concerning mercy,” means that the worshipper may ask for mercy when he passes by a verse concerning mercy. For example, when Paradise is mentioned, he may say, “O Allah, I ask You for Paradise.” He may also ask Him for His bounty. If he passes by praise of the prophets, the righteous allies of Allah, or the like, he may say, “I ask Allah for His bounty,” or, “I ask Allah to join me with them,” or something similar.
His statement, “even in an obligatory prayer,” indicates a difference of opinion: may he do this in an obligatory prayer, or may he not? (1)
The correct view is that stated by the author: he may do so, because this is simply supplication, and there is nothing wrong with supplication during the prayer. Thus, he may seek refuge when he comes across a verse of warning and ask when he comes across a verse concerning mercy, even if he is performing an obligatory prayer.
The evidence is the hadith of Hudhayfah ibn al-Yaman, may Allah be pleased with him: he prayed with the Prophet, peace and blessings be upon him, one night, and the Prophet recited al-Baqarah, al-Nisa, and Al Imran. Whenever he came across a verse concerning mercy, he would ask; and whenever he came across a verse of warning, he would seek refuge. (2) This was an act of the Messenger, peace and blessings be upon him, and the basic principle is that he is an example for us, and that we may follow what he did unless there is evidence to the contrary. If someone says, “This occurred in a voluntary prayer, so what is your evidence that it is permissible in an obligatory prayer?”
The answer is that whatever is established in a voluntary prayer is also established in an obligatory prayer, unless there is evidence otherwise. Here, there is no evidence distinguishing between an obligatory and a voluntary prayer.