Do we have to recite the chapters of Quran mentioned in the hadith together? For example, surah Az-Zumar and surah Israa or all the musabihaat?Is it permissible to recite only one surah that is mentioned in one hadith such as surah Zumar or surah Al-Hashr? Do you have to recite them when lying in bed or can you do it somewhere else then go to sleep?
If you can recite all the musabihat according to the hadith then it is good. If you cannot, you may say the chapters, or recite ayah Al-Kursi or say some of the supplications before sleeping.
Try to say as much as you are able to. These remembrances are Sunnah from mustahabat: it means it is not obligatory rather highly recommended.
Sheikh Abdul-Muhsin Al-Abbad explained that the sleeping remembrances should be said when we go to bed.
He said, “if you started your remembrances and you left your bed to do something and it took a long time before you returned to bed, you would have to repeat what you said before you sleep, and if you started to make the remembrances in bed and you left your bed and returned within a short period of time, then you can continue and do not repeat what you already said of the remembrances.”