What is the interpretation of the second-to-last verse of Surat Fussilat: "We will show them Our signs in the horizons and within themselves until it becomes clear to them that it is the truth"? And does the verse mean that disbelievers will know that Islam is the truth before their death so that they will have no excuse on the Day of Resurrection? And what is the authenticity of the Hadith mentioned in Musnad Ahmad concerning Allah's test for those whom the message of Islam has not reached?

The interpretation of the noble verse (We will show them Our signs in the horizons and within themselves until it becomes clear to them that it is the truth) indicates Allah’s promise to reveal His signs in the vast universe (horizons) and in the nature and composition of humankind (within themselves) to prove the truth of the Qur’an and Islam. “Horizons” encompasses the signs of the heavens and the earth, such as planets and natural phenomena, or the Islamic conquests that demonstrated Allah’s support for His Messenger. As for “within themselves,” it includes the miraculous creation of humans, or the events that befell the disbelievers, such as the Battle of Badr and the conquest of Mecca. The verse deals with multiple meanings that are not contradictory, and Allah has fulfilled His promise by displaying these signs throughout the ages, and new signs continue to be revealed, confirming that Islam is the truth, the Qur’an is the truth, and the Messenger Muhammad, peace be upon him, is the truth. Despite the clarity of these signs, many people do not reflect upon them or stubbornly resist the truth, while there is a group to whom the call has not reached or who had an excuse, and they will be tested on the Day of Resurrection.