Is it permissible to combine the post-prayer remembrances (dhikr) so that one says: "There is no god but Allah, He is One, without partner. To Him belongs all sovereignty and all praise, and He is over all things competent. O Allah, there is none to withhold what You have given, and none to give what You have withheld, and the might of the mighty benefits not against You. There is no might nor power except with Allah. There is no god but Allah, and we worship none but Him. To Him belong all blessings, and all bounty, and all good praise. There is no god but Allah, sincere in devotion to Him, even if the disbelievers detest it"?

The two hadiths mentioned in the question, namely: "There is no god but Allah alone, without partner. To Him belongs all sovereignty and all praise, and He is over all things competent. O Allah, there is none to withhold what You have given, and none to give what You have withheld, and the might of the mighty benefits them not against You," and "There is no might and no power except with Allah. There is no god but Allah, and we worship none but Him. To Him belong all blessings, and all grace, and all good praise. There is no god but Allah, sincere in devotion to Him, even if the disbelievers detest it," are authentic and sound.

Many scholars have combined these two forms of remembrance, including the two Sheikhs Ibn Baz and Ibn 'Uthaymeen, may Allah have mercy on them, in the supplications recited after prayer. It is preferable to repeat the tahlil (utterance of "La ilaha illa Allah") twice, but the matter is flexible if they are combined.