Can one pray the two rak'ahs of the Fajr supererogatory prayer as four rak'ahs, and is it obligatory to denounce the one who does so?

The Fajr ratibah (supererogatory prayer) consists of two rak'ahs. Scholars have differed regarding the ruling on praying after the dawn breaks, other than these two rak'ahs.

The majority of scholars are of the opinion that it is prohibited to pray after the dawn breaks, except for two rak'ahs, based on the hadith of Ibn 'Umar, may Allah be pleased with him: "Do not pray after Fajr except for two prostrations." And based on the action of the Prophet, peace and blessings be upon him, for Hafsah, may Allah be pleased with her, said: "When the dawn broke, the Messenger of Allah, peace and blessings be upon him, would not pray except two light rak'ahs."

Others are of the opinion that it is permissible to pray, and An-Nawawi detailed three views: it is makruh (disliked), or it is not makruh until one prays the sunnah of Fajr, or it is not makruh until one prays the obligatory Fajr prayer. He favored the last view.

As for Shaykh al-Islam Ibn Taymiyyah, he chose the permissibility of praying after the dawn breaks, even more than two rak'ahs, on condition that this is not taken as a regular habit or a consistent sunnah, and that it is said, "There is no sunnah after the dawn breaks except for two rak'ahs," and not "There is no general prohibition."

The more cautious approach is for the worshiper to limit himself to two rak'ahs after the dawn breaks, in adherence to the practical Sunnah, and there is no prohibition from increasing, but on condition that it is not taken as a habit.