Praise be to Allah.
We do not think that the khateeb on Friday should come down from the minbar during his khutbah, or that he should interrupt the khutbah in order to do the prostration of gratitude in the manner mentioned in the question. That is for the following reasons:
The prostration of gratitude is only recommended when a blessing comes suddenly, as the fuqaha’ stated, by which they mean that it is a new blessing that comes suddenly, with which Allah may honour a Muslim after it had been delayed. What you mention in your khutbah of the blessings of Allah, may He be exalted, and examples of the mercy that He bestows upon people are ongoing or previous blessings that are constantly renewed, but they do not come anew after not having been there. Hence it is not recommended to do the prostration of gratitude in that case.
Al-Khateeb ash-Sharbeeni (may Allah have mercy on him) said:
It is Sunnah when a new blessing comes, such as when a child is born, or one attains high status, or acquires wealth, or one who was away returns, or when victory is granted over an enemy, or when calamity is warded off, such as being saved from burning or drowning. That is because of the report narrated by Abu Dawood and others, that when news came to the Prophet (blessings and peace of Allah be upon him) of something that made him happy, he would fall down in prostration. What is excluded by the phrase “new blessing” is blessings of an ongoing nature, such as good health, being Muslim or being independent of means, because that would lead to spending one’s entire life in prostration. In at-Tanbeeh and al-Muhadhdhab, the authors restricted the prostration of gratitude to being for new blessings, and the author narrated it in his commentary from ash-Shaafa‘i and his companions, that it should be restricted to cases of new blessings or being saved from calamity that should be apparent, so as to exclude hidden blessings, such as attaining knowledge or concealment of some bad deed. Another condition was added in Asl ar-Rawdah and al-Muharrar, based on the verse in which Allah says (interpretation of the meaning): “from (sources) he never could imagine” [at-Talaaq 65:3]. It says in al-Muhimmaat: but this condition may be subject to further discussion. From what was said concerning this issue, it should be understood that it makes no difference whether the person was the cause of this blessing or not. Therefore it was not discussed in al-Majmoo‘. And that is more appropriate. Hence Ibn al-Muqri did not refer to it at all.
End quote from Mughni al-Muhtaaj (1/447); see also Tuhfat al-Muhtaaj (2/216)
Al-Bahooti al-Hanbali (may Allah have mercy on him) said:
It is mustahabb to do the prostration of gratitude when a new blessing that is visible occurs or visible harm is warded off, that would have affected the individual and other people, or would have affected him only, as is indicated in some texts. Examples of that include the birth of a new child, new wealth, attaining new status or achieving victory over an enemy. If we did not stipulate that the blessing should be apparent and visible, (the prostration of gratitude would never cease) because the blessings of Allah at all times are innumerable. Therefore wise people congratulate one another on being saved from some harm that could have befallen them, but they do not do that all the time.
End quote from Kashshaaf al-Qinaa‘ (1/449-450)
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said:
When a new blessing comes – this excludes ongoing blessings, because in the case of an ongoing blessing, if we were to tell someone that it is mustahabb to prostrate in gratitude for it, he would be constantly prostrating, because Allah says (interpretation of the meaning): “and if you count the Blessings of Allah, never will you be able to count them” [Ibraaheem 14:34]. Ongoing blessings are always with a person, such as the soundness of his hearing and vision, his ability to speak clearly, and physical health – all of these are blessings; breathing is another blessing, and so on. But there is no report in the Sunnah to suggest that one should prostrate in gratitude for such blessings.
End quote from ash-Sharh al-Mumti‘ (4/105)
We also think that even if the blessing is new, it is not appropriate to do the prostration of gratitude for it on the minbar, as the fuqaha’ have stated that the prostration of gratitude should not be done during the prayer, and they said that an analogy cannot be drawn with the permissibility of doing the prostration of recitation during prayer or on the minbar. That is because there is no report that speaks of the Prophet (blessings and peace of Allah be upon him) doing the prostration of gratitude during prayer or on the minbar.
When some scholars – especially the Maalikis – argued that the whole idea of the prostration of gratitude is not prescribed at all, based on the hadith of Anas ibn Maalik (may Allah be pleased with him), according to which, when a man came to the Prophet (blessings and peace of Allah be upon him) and complained to him about the drought when he was on the minbar, he raised his hands, and we could not see any cloud in the sky, but by the One in Whose hand is my soul, he did not lower his hands before there appeared clouds like mountains. And before he even came down from the minbar we saw the rain dropping from his beard (blessings and peace of Allah be upon him).
Narrated by al-Bukhaari in his Saheeh (933) and by Muslim in his Saheeh (897). They said: But he (blessings and peace of Allah be upon him) did not do the prostration of gratitude even though there was a new blessing that appeared at that time.
Imam an-Nawawi (may Allah have mercy on him) responded to that by saying:
The response to their argument is that he did not do this prostration in some instances to highlight that it is permissible not to do it, or because he was on the minbar and prostrating is difficult in that situation, or because the prostration in prayer is sufficient. In fact the answer may be all of the above; we should accept one of these answers, or any other answer, in order to reconcile between the reports.
End quote from al-Majmoo‘ (4/70)
The fact that there is no report to suggest that the Prophet (blessings and peace of Allah be upon him) did not do the prostration of gratitude on the minbar, even though there was a new blessing that occurred at that time, may indicate that it is not permissible for the khateeb to do that in that situation.
In fact, what this man did could be taken as introducing something that was never done at the time of the Prophet (blessings and peace of Allah be upon him), because it is not narrated in the Sunnah, nor was it the practice of the early generations, and it was not known among the people. Such a thing is more likely to be bid‘ah (innovation) than Sunnah, and it is more akin to seeking fame and attention than striving to be humble and discreet in worship.
For more information on the rulings on the prostration of gratitude, please see question no. 140804.
And Allah knows best.