The Companions (may Allah be pleased with them) were extremely keen on following the Prophet's Sunnah. They were quite aware of the details of his honorable Sunnah, what he used to recite in every prayer and whether he lengthened or shortened it, etc. In this Hadīth, ‘Abdullah ibn ‘Abbās (may Allah be pleased with him and his father) reports that the Prophet (may Allah's peace and blessings be upon him) used to regularly recite Surat as-Sajdah in the first Rak'ah (unit of prayer) of the Fajr prayer every Friday. In contrast, in the second Rak'ah, he used to recite Surat al-Insān: {Was there not a period of time when man}. The reason behind this could be what is included in these two Surahs mentioning what happened and what will happen in the beginning and the Hereafter, like the creation of Adam (peace be upon him), gathering the creatures and resurrecting them from the graves to Paradise and Hellfire, the situations of the Day of Judgment, which will occur on Friday. Ibn' Abbās (may Allah be pleased with him and his father) also reports that the Prophet (may Allah's peace and blessings be upon him) used to recite Surat al-Jumu'ah in the first Rak'ah of the Friday prayer, and in the Second Rak'ah he used to recite Surat al-Munāfiqūn. The reason behind this could be the fact that Surat al-Jumu'ah makes a mention of the Friday prayer and its high status and because Surat al-Munāfiqūn rebukes the hypocrites and urges them to repent since they used to attend the Friday prayer with the Prophet (may Allah's peace and blessings be upon him) and used to gather therein, so, perhaps what is in this Surah would act as a deterrent, an alert, and a warning for them..