Is it permissible to combine two supplications from the opening prayers (Du'a Al-Istiftah)?

The default in the Sunnah (definition) is to limit oneself to one opening supplication (Du'a al-Istiftah), and not to combine more than one supplication in a single prayer. The Prophet, peace and blessings be upon him, was asked what he says between the Takbir and the recitation, and he responded by mentioning a single supplication.

Some scholars have gone to the extent of permitting the combination of opening supplications, and among them are those who deemed it recommended for the individual (praying alone) and the Imam if the congregants permit him.

However, the preferred approach is to vary the opening supplications between prayers, so one supplicates with one supplication at one time and with another at another time. This is because it is a matter of variety. If one combines them, there is a difference of opinion regarding it, and the most preferable and cautious approach is to limit oneself to what has been authentically transmitted.