Is the Sunnah prayer before Dhuhr (the noon prayer) to be performed as two units (rak'ahs) with two salutations, or as four units (rak'ahs) with one salutation, in accordance with the Hadith: "The prayer of the night and day is two by two"?

Night and day prayers are two rak'ahs by two rak'ahs (i.e., prayed in sets of two), and this is the madhhab of Shafi'i, Ahmad, and Malik. If one prays them as four rak'ahs with a single taslim, that is permissible, and this is the opinion of some scholars like Sufyan al-Thawri, Ibn al-Mubarak, and Ishaq. However, it is preferable to give taslim after every two rak'ahs in the supererogatory prayers and others.