All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.{C}
First of all, we ask Allah to increase your zeal about the recitation of the Quran, and to enable you to do all that is good.
Reciting the entire Quran according to the order of the Mus-haf [the hardcopy of the Quran] is better than repeating certain Soorahs.
Shaykh Ibn Taymiyyah said:
“If a person recites Soorah Al-Ikhlaas {Say, "He is Allah, [who is] One} [Quran 112], he gets the reward of reciting one third of the Quran. However, this does not mean that the reward is the same as that which is obtained when one actually recites one third of the Quran [..] the knowledge he obtains by reciting the entire Quran is not obtained by merely reciting this Soorah. Therefore, the one who recites the entire Quran is better than the one who recites Soorah Al-Ikhlaas three times, because of the variety of the reward.” [End of quote]
In addition to this, reciting the entire Quran according to the order of the Mus-haf is better.
An-Nawawi said in his book At-Tibyaan:
“The scholars said that it is best to recite according to the sequence of the Mus-haf. So he recites Al-Faatihah, then Al-Baqarah, then Aal 'Imraan, and then what follows it according to the sequence, whether he recited in the prayer or outside the prayer ...” [End of quote]
Your friend constantly reciting Soorah Al-Mulk [Quran 67] is permissible as there is a confirmed Islamic text about it. Jabir narrated that the Prophet would not sleep until he recites Soorah As-Sajdah [Quran 32] and Soorah Al-Mulk [Quran 67]. [Al-Albaani classified it as authentic]
On the other hand, there is a Hadeeth about Soorah Al-Waaqi’ah, that reads: “Whoever recites Soorah Al-Waaqi’ah [Quran 56] every night, he will never be befallen by poverty.” This is an inauthentic or fabricated Hadeeth, as stated by Shaykh Al-Albaani in his book As-Silsilah Adh-Dha’eefah.
Hence, if your friend does not believe that it is a Sunnah to recite Soorah At-Tawbah [Quran 9] and Soorah Al-Waaqi’ah [Quran 56], then he is not sinful. However, if he believes that reciting them at this particular time is a Sunnah, then this is a religious innovation. Ibn ‘Uthaymeen said:
“If there is no Islamic text about the recitation of some Soorahs or verses, then it is not permissible for a person to recite them while believing that reciting these particular Soorahs or verses is a Sunnah.” [End of quote]
We advise you to persist in the recitation of the Quran, and advise your friend in a soft and gentle manner, and clarify to him that it is better for him to recite the entire Quran more than what he does now.
Allah knows best.