The du‘aa’ “O Allah, I ask you for the best of what Your slave and Prophet Muhammad (blessings and peace of Allah be upon him) asked You for…” is a concise supplication
Question

There are many supplications that are narrated from the Prophet (blessings and peace of Allah be upon him), and it is difficult for me to remember all of them, because my memory is not good enough. But there is a supplication (du‘aa’) that is narrated in Riyadh as-Saaliheen, in Book 17, hadith no. 1492, which I like very much and I would like to focus on it and memorise it. Is it a saheeh hadith, and is memorising only this supplication sufficient?
This is the text: “O Allah, I ask You for the best of what Your Prophet Muhammad (blessings and peace of Allah be upon him) asked You for, and I seek refuge with You from the worst of that from which Your Prophet Muhammad (blessings and peace of Allah be upon him) sought refuge with You, for You are the One Whose help is to be sought, and we seek Your help to attain what we aspire for, and there is no power and no strength except with Allah.”
Praise be to Allah.It was narrated from ‘Aa’ishah (may Allah be pleased with her) that the Messenger of Allah (blessings and peace of Allah be upon him) taught her this supplication:
“Allaahumma inni as’aluka min al-khayri kullihi, ‘aajilihi wa aajilihi, ma ‘alimtu minhu wa maa lam a‘lam. Wa a‘oodhu bika min al-sharri kullihi, ‘aajilihi wa aajilihi, ma ‘alimtu minhu wa maa lam a‘lam. Alllaahumma inni as’aluka min al-khayri ma sa’alaka ‘abduka wa nabiyyuka Muhammadun sall Allahu ‘alayhi wa sallam, wa a’oodhu bika min sharri ma ‘aadha bihi ‘abduka wa nabiyyuka. Allaahumma inni as’aluka al-jannah wa ma qarraba ilayha min qawlin aw ‘amal, wa a‘oodhu bika min al-naar wa ma qarraba ilayha min qawlin aw ‘amal, wa as’aluka an taj‘ala kulla qadaa’in taqdeehi li khayraan (O Allaah, I ask You for all that is good, in this world and in the Hereafter, what I know and what I do not know. O Allaah, I seek refuge with You from all evil, in this world and in the Hereafter, what I know and what I do not know.  O Allaah, I ask You for the good that Your slave and Prophet Muhammad (blessings and peace of Allah be upon him) has asked You for, and I seek refuge with You from the evil from which Your slave and Prophet sought refuge. O Allaah, I ask You for Paradise and for that which brings one closer to it, in word and deed, and I seek refuge in You from Hell and from that which brings one closer to it, in word and deed. And I ask You to make every decree that You decree concerning me good).”
Narrated by Ahmad in his Musnad (24498) and Ibn Maajah in his Sunan (3846). Classed as saheeh by al-Albaani in Saheeh al-Jaami‘ (1276).
With regard to the wording, “O Allah, I ask You for the best of what Your Prophet Muhammad (blessings and peace of Allah be upon him) asked You for, and I seek refuge with You from the worst of that from which Your Prophet Muhammad (blessings and peace of Allah be upon him) sought refuge with You, for You are the One Whose help is to be sought, and we seek Your help to attain what we aspire for, and there is no power and no strength except with Allah,” this was narrated by at-Tirmidhi (3521) and by al-Bukhaari in al-Adab al-Mufrad (679). It was classed as da‘eef (weak) by al-Albaani in Da‘eef at-Tirmidhi.
So the reliable version is the first one, which is sufficient and there is no need for the second version. It is recommended to memorise it and to call upon Allah with these words, and to do so frequently, because it is a concise supplication.
But if you recite the second version, there is nothing wrong with that. We have stated previously in the answer to question no. 179426 that if a supplication is good and appropriate, and the meaning of the words is sound, then it is permissible to call upon Allah with these words, even if it was narrated in a da‘eef hadith.
This du‘aa’ is one of the most concise of supplications, if not the most concise of them, for it is asking for all that is good and seeking refuge with Allah from all that is evil. Moreover, it is asking for the best of good things, which is Paradise and the righteous deeds that bring one close to it, and it is seeking refuge with Allah from the worst of evil things, which is the Fire and the sins that bring one close to it.
Al-Mulla ‘Ali al-Qaari said in Mirqaat al-Mafaateeh (1739):
The most concise supplication that has been narrated is… Then he quoted this du‘aa’. End quote.
Al-Minnaawi said in Fayd al-Qadeer (2/162):
Al-Haleemi said: This comes under the heading of concise words that the religious texts recommend to use in supplication because if a person recites these words in supplication, then he has asked Allah for all that is good and has sought refuge with Him from all that is evil. If a person limits himself to asking only for a particular good thing or to ward off a particular bad thing, then he is falling short with regard to himself. End quote.
It was narrated that ‘Abdullah ibn Mas‘ood (may Allah be pleased with him) used to recite this supplication after the tashahhud in prayer, and he used to teach it to people. Al-Haafiz Ibn Hajar (may Allah be pleased with him) said in Fath al-Baari:
There are several reports which mention what may be said after the tashahhud, one of the best of which is the report narrated by Sa‘eed ibn Mansoor and Abu Bakr ibn Abi Shaybah via ‘Umayr ibn Sa‘d who said: ‘Abdullah – i.e., ibn Mas‘ood – used to teach us the tashahhud in the prayer, then he would say: When  one of you has finished reciting the tashahhud, then let him say: “O Allah, I ask you for all that is good, what I know and what I do not know, and I seek refuge with You from all that is evil, what I know and what I do not know. O Allah, I ask You for the best of what Your righteous slaves ask you for, and I seek refuge with You from the worst of what Your righteous slaves seek refuge with You from. Our Lord, give us in this world what is good…” and he [Ibn Mas ‘ood] used to say: No Prophet or righteous person ever offered a supplication but it is implied in this supplication. End quote.
This supplication is sufficient, and if a Muslim recites it a great deal then he will attain much good. There is nothing wrong with a Muslim limiting himself to this, if he is not able to recite other concise supplications and it is difficult for him to memorise them.
But if one is able to do so, then undoubtedly it is better to memorise what he knows of concise supplications of the Prophet (blessings and peace of Allah be upon him), and to vary them as much as possible, and to pray for himself however he wishes as well, for the good of this world and the hereafter.
And Allah knows best.