Because the Day of Resurrection is imminent and inevitable, Allah has likened it to “tomorrow.” He, the Exalted, says, “And let every soul look to what it has sent ahead for tomorrow.” ⦗1⦘ Here, “tomorrow” means the day that follows your own. He also says, “They see it as far-off, but We see it as near.” ⦗2⦘
Al-Tirmidhi records—and classifies as authentic—a ḥadīth traced back to Anas in which the Prophet (peace and blessings be upon him) said, “I and the Hour have been sent like these two,” and he held up his index and middle fingers.
In the two Ṣaḥīḥs it is reported from ʿUmar (may Allah be pleased with him), in a marfūʿ ḥadīth: “Your allotted span, compared with the nations before you, is from the ʿAṣr prayer until the setting of the sun.” Another wording reads, “Your remaining time, in relation to the nations before you, is what lies between the ʿAṣr prayer and sunset.”
Because the affair of the Hour is so momentous, concern for it surpasses all else. For this reason the Prophet (peace and blessings be upon him) frequently explained its portents and signs, informed his community of the tribulations that will precede it, and alerted and warned them so that they might make ready.
As for the exact moment of its arrival, that is knowledge Allah alone possesses. He has concealed it from His servants for their own benefit, that they might stay in constant readiness—just as He, Exalted be He, has hidden from every soul the time of its own death so that people remain ever prepared and watchful, never lax in doing good works.
The scholar al-Saffārīnī said: “Know that the portents of the Hour fall into three categories. One has already appeared and passed; these are the distant signs. Another has appeared but has not yet ceased; rather, it continues to increase. The third comprises the major signs that will be followed directly by the Hour, and they will come in quick succession like beads cascading after their string has snapped.”
The first category—those signs that have already appeared and ended—includes: the Prophet’s mission, his death, and the conquest of Jerusalem.