Is it permissible to be content with memorizing three parts of the Quran?

We advise you, after fearing Allah, not to stop at memorizing parts of the Quran, but rather to elevate your ambition to memorize the entire Quran; in order to achieve what the Prophet (peace be upon him) promised to the memorizers of the Book of Allah and their parents. Imam Ahmad narrated from Buraydah (may Allah be pleased with him) that the Prophet (peace be upon him) said: "Learn Surat Al-Baqarah, for taking it is a blessing, and leaving it is a regret, and the magicians cannot overcome it." Then he said: "Learn Surat Al-Baqarah and Al Imran, for they are the two bright ones, they will shade their companion on the Day of Resurrection as if they were two clouds or two shades or two flocks of birds in ranks." He added: "Indeed, the Quran will meet its companion on the Day of Resurrection like a pale man, and it will say to him: Do you recognize me? He will say: I am your companion, the Quran, who made you thirsty during the midday heat and kept you awake at night. Then he will be given sovereignty in his right hand and eternity in his left, and a crown of dignity will be placed on his head, and his parents will be clothed with two garments that the people of this world would not be able to afford. It will be said: This is because your child took the Quran. Then it will be said to him: Recite and ascend in the degrees of Paradise and its chambers. He will continue to ascend as long as he recites, whether by reading or by chanting." Despite this virtue, there is no objection to memorizing only certain parts or surahs.