What is the ruling on the Sunnah of Zawwal just before noon, and what is its evidence from the Sunnah?

Scholars have differed concerning the four rak'ahs prayed after zawal (the sun's declination from its zenith) and before Dhuhr (midday prayer). Some have affirmed their legitimacy as a prayer independent of the pre-Dhuhr sunnah, citing the hadith of Abdullah ibn As-Sa'ib that the Prophet (peace be upon him) used to pray four rak'ahs after the sun declined and would say: "Indeed, it is a moment when the gates of heaven are opened, and I love that a righteous deed ascends for me therein." Other scholars are of the view that these are the pre-Dhuhr sunnah.