For the first question, there is a hadith reported on the authority of Jabir ibn ‘Abdullah who said:

I heard Allah’s Messenger (peace be upon him) as saying this one month before his death: You asked me about the Last Hour whereas its knowledge is with Allah. I, however, take an oath and say that none upon the earth, the created beings, would survive at the end of one hundred years. (Muslim)

Some people thought that the Last day is supposed to be within one hundred years after the Prophet said this hadith. But the correct meaning of this hadith is explained by the other version which is also related by Abu Sa῾īd al-Khudrī who reported the Prophet’s saying, “There would be none amongst the created beings living on the earth (who would survive this century).” (Muslim) Therefore, the Prophet meant that his companions who were living when he issued this hadith would not live more than one hundred years.

For the second question, Li῾an and Mula`ana are synonymous. They are derived from La`n (to curse). Technically it is an act of a husband’s swearing before a judge that he witnessed his wife committing adultery and fails to prove it with four witnesses. It is fully explained in Quran 24:4. The occasion of revelation for this verse is that when Hilal ibn Umayyah (may Allah be pleased with him) accused his wife of adultery, the Messenger of Allah (peace be upon him) asked him to prove it with four witnesses and said that the punishment of slandering (qadhf) would be applied if he could not prove it. He repeated it several times. Hilal ibn Umayyah said, “O Messenger of Allah! One of us sees his wife committing adultery with a man; you ask us for evidence. I swear by Allah, who sent you as a true prophet, that I am telling the truth. I believe that Allah will send down a verse to you that will save my back from these stripes.” (Al-Bukhari, Muslim, Abu Dawud, and Ahmad)

Thereupon, the following ‘verse of mula`anah’ was sent down:

“And for those who launch a charge against their spouses, and have (in support) no evidence but their own― their solitary evidence (can be received) if they bear witness four times (with an oath) by Allah that they are solemnly telling the truth; And the fifth (oath) (should be) that they solemnly invoke the curse of Allah on themselves if they tell a lie. But it would avert the punishment from the wife, if she bears witness four times (with an oath) by Allah, that (her husband) is telling a lie; And the fifth (oath) should be that she solemnly invokes the wrath of Allah on herself if (her accuser) is telling the truth.” (An-Nur 24:6-9)

There are two reasons for li`an: The first one is when a man accuses his wife of adultery which necessitates the application of the punishment of adultery when the accusation is made for a woman who is not a relative of his. The second one is when the father rejects (does not accept) that he is the father of the child that has not been born yet or that was born.