This will be after every bowing (ruku‘) after which there is recitation, or after the last bowing of every unit (rak‘ah) after which there are prostrations (the tahmid will be said).

Lady Aisha (may Allah be pleased with her) narrates that during the blessed life of the Messenger of Allah (peace and blessings be upon him), there was a solar eclipse, so he went to the mosque and stood up (for prayer) «‏‏‏‏اللهُ أَكْبَرُ» ‏‏‏‏ said. And the people formed rows behind him. The Messenger of Allah (peace and blessings be upon him) recited a very long recitation. Then «‏‏‏‏اللهُ أَكْبَرُ» ‏‏‏‏ said and performed a long bowing (ruku). Then he raised his blessed head from the bowing and «‏‏‏‏سَمِعَ اللهُ لِمَنْ حَمِدَهُ، رَبَّنَا وَلَكَ الحَمْدُ» ‏‏‏‏ said. Then the Messenger of Allah (peace and blessings be upon him) stood and recited for a long time, but it was less than the first recitation. Then the Messenger of Allah (peace and blessings be upon him) said «‏‏‏‏اللهُ أَكْبَرُ» ‏‏‏‏ and performed a long bowing, and this bowing was shorter than the first one. Then the Messenger of Allah (peace and blessings be upon him) said «‏‏‏‏سَمِعَ اللهُ لِمَنْ حَمِدَهُ، رَبَّنَا وَلَكَ الحَمْدُ» ‏‏‏‏. Then he performed the second rak'ah in the same manner. In this way, the Messenger of Allah (peace and blessings be upon him) completed four bowings and four prostrations. Before the Messenger of Allah (peace and blessings be upon him) finished the prayer with salam, the sun had already become bright. Then the Messenger of Allah (peace and blessings be upon him) stood and delivered a sermon and praised and glorified Allah as is befitting to His majesty. Then he said: "Indeed, the sun and the moon are two signs among the signs of Allah. They do not eclipse due to the death or life of any person. Therefore, when you see an eclipse of either of them, hasten to perform prayer."