Is it just combining Maghrib (Sunset)

Q 7: what are the conditions for combining two Salahs (Prayers)? Should the supererogatory Salah or witr (Prayer with an odd number of units) be performed in case of combining Salah?

(Part No. 8; Page No. 144) A: Combining two Salahs is permissible for the travelers or the sick persons, and for those at home on a rainy night. They may perform Witr after combining the `Isha' (Night) and Maghrib (Sunset) Prayers at the earlier time (i.e. During the time for Maghrib).May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.