How many are the Sunnahs of prayer, and what are the pre- and post-prayer Sunnahs, and why do worshippers differ concerning the Sunnah of Dhuhr?

The differing practices of worshippers regarding the supererogatory (Sunnah) prayers of Dhuhr stem from the various narrations reported concerning this matter. Thus, whoever prays two rak'ahs before it and two rak'ahs after it has conformed to the narration of Ibn Umar. And whoever prays four rak'ahs before it and two rak'ahs after it has conformed to the narration of Aisha. And whoever consistently prays four rak'ahs before it and four rak'ahs after it has achieved perfection.