Tafsir of Al-Hijr 15:98

(So exalt [Allah] with praise of your Lord) Meaning: Turn to your Lord for whatever distress or constriction of the chest befalls you, by means of exaltation (Tasbih), while accompanied by His praise. That is, say: Subhan-Allah wa-l-hamdu-lillah (Glory be to Allah, and praise be to Allah). Or, declare Him far removed from what they say, while praising Him—Glory be to Him—for guiding you to the truth. Thus, "Tasbih" and "Hamd" are taken in their linguistic meanings, whereas in the first interpretation, they are taken in their customary/terminological meanings, namely, the utterance of those two phrases. The presentation of the title of Lordship, along with the attribution to His pronoun—may the blessings and peace of Allah be upon him—contains a hidden gentleness toward him, and an indication of the cause of the command, which is the aforementioned order.

(And be among those who prostrate) Meaning: Those who pray. In this, the part is used to express the whole, and this part—according to the view of some—is the most excellent of the parts [of prayer], due to what has been authentically narrated: "The closest a servant is to his Lord is when he is prostrating." This is not a place of prostration (Sajdah), contrary to the view of some.

In His commanding him—may the blessings and peace of Allah be upon him—with what has been mentioned, there is guidance to that by which the grief he finds within himself might be unveiled. It is as if it were said: "Do this, and your Lord will uncover from you the grief and distress you find in your chest." Because of the greater concern for the matter of prayer, the command to perform it was brought in a manner—as you see—different from the previous command, in this specific form. In this, there is an encouragement toward it that is not hidden. Indeed, whenever a matter saddened the Prophet—may the blessings and peace of Allah be upon him—he would turn to prayer. It has been authentically narrated: "There have been made beloved to me from your world, women and perfume, and the coolness of my eyes has been placed in prayer."

Some have mentioned that the verse contains an indication encouraging prayer in congregation, and that the failure to qualify "prostration" with an object like "to Him" or "to your Lord" is an indication that it hardly crosses the mind to perform it for anyone other than the Exalted. So reflect upon this.