Is the preacher's saying between the two sermons, "I say this and ask Allah for forgiveness for myself and for you, so O the success of those who seek forgiveness, seek Allah's forgiveness," a Sunnah? And what is the meaning of "O the success of those who seek forgiveness, seek Allah's forgiveness"? And what is it prescribed for the listeners to do after this saying?

The meaning of "O the triumph of those who seek forgiveness" is "O their happiness," and it is an encouragement to seek forgiveness and an expression of wonder at the abundance of its reward. This phrase has not been reported in the Sunnah.

As for the khateeb (preacher) seeking forgiveness for himself and for the worshippers and encouraging them to do so at the end of the Friday sermon, this is permissible. Many scholars have explicitly stated the desirability of concluding the sermon with seeking forgiveness, citing the actions of the Prophet, peace and blessings be upon him, and the statements of jurists like Ibn al-Qayyim, al-Hattab, and an-Nawawi.

Regarding the listener, it is permissible for him to supplicate with whatever he wishes or remember Allah with any dhikr he desires between the two sermons, and to face the Qiblah with his supplication, because this time is a time when prayers are answered, as mentioned by Ibn Uthaymeen. There is no specific remembrance or supplication mentioned in tradition for between the two sermons, but it is a time when prayers are answered for the good of this world and the Hereafter for both the listener and the Imam.