What is the ruling regarding the permissibility of combining remembrances (dhikr)?

The default rule is the permissibility of emulating the Prophet, peace and blessings be upon him, in all established supplications and invocations that have been reported from him. It is recommended to combine them for an individual, or for an Imam if the congregants permit him. Otherwise, it is advisable to vary them so that none of them are abandoned.

Al-Nawawi said: It is recommended for the individual and the Imam to combine the opening supplications if the congregants permit him; otherwise, he should limit himself to some of them.

Al-Nawawi also said: It is recommended to combine the invocations of bowing (rukūʿ) if possible, prioritizing the glorification (tasbīḥ). If one limits himself to some of them, he should vary them over time.

Ibn ʿAllan said: Combining the various invocations in bowing, prostration (sujūd), and other positions is preferable, and its preference is not contradicted by the fact that they were not reported together in one single hadith.

It is stated in "Kashshāf al-Qināʿ": There is no dislike in adding to the reported invocations in bowing and prostration from supplications that have been reported.

Ibn ʿUthaymīn held that the invocations of bowing should be combined, unlike the opening supplications.

Shaykh Salih Al-Usaimi stated that all invocations are to be recited if the context allows it, such as the invocations of bowing, prostration, morning, and evening. However, one should limit oneself to a single invocation if the context does not allow for more, such as the opening supplication.

In conclusion: The default rule is the recommendation of combining invocations for whoever is able to do so.