What is the opening supplication (Du'a al-Istiftah) for the night vigil (Qiyam al-Layl) and Tahajjud prayer after the تكبير (Takbir), and is it recited in every two rak'ahs or only in the first two rak'ahs, and are they considered one opening supplication if they are one?

The opening supplication (Du'a al-Istiftah) is prescribed in the night prayer (Salat al-Layl) and Tahajjud. It is permissible to use the opening supplications mentioned for the obligatory prayers, or those specific to the night vigil prayer, such as the supplication: "O Allah, to You be praise, You are the Light of the heavens and the earth and all that is within them..." or the supplication: "O Allah, Lord of Jibreel, Mika'il, and Israfeel...". Scholars have not differentiated between Tahajjud prayer and the general night prayer regarding the opening supplication, although Ibn 'Uthaymeen mentioned that the opening supplication for Tarawih differs from Tahajjud, but he did not clarify his evidence. It is recommended to repeat the opening supplication in every set of two rak'ahs (tasleema) of the night prayer, especially Tarawih, because each tasleema is considered an independent prayer. Ibn 'Uthaymeen and the Permanent Committee have favored this view. Scholars have differed on the permissibility of combining more than one opening supplication in a single prayer; some, like Imam An-Nawawi, deemed it desirable, while others saw no legal basis for it.