Praise be to Allaah.
If he says Hayya ‘ala al-Falaah (come to prosperity)
before Hayya ‘ala al-salaah (come to prayer), he has to repeat
Hayya ‘ala al-Falaah (come to prosperity) after saying Hayya ‘ala
al-salaah (come to prayer), because it is essential that the phrases of
the adhaan be given in the right order. The adhaan was narrated in this
particular order, so if a person inverts the phrases, he is doing something
that is not in accordance with the command of Allaah and His Messenger, and
the Prophet (peace and blessings of Allaah be upon him) said: “Whoever
does something that is not in accordance with this matter of ours will have it rejected.” End quote.
Fataawa al-Tahaarah wa’l-Salaah by Shaykh Ibn ‘Uthaymeen (p. 63).