This "news" has been all over the Palestinian Arab media for months, ever since Ha'aretz publicized an unsourced claim that the 18th century sage the Vilna Gaon had predicted the building of the Third Temple today, Rosh Chodesh Nisan.
Some PalArabic media have even been publishing a photo of the cornerstone that Israel supposedly is planning to place today.
Palestine Today mistranslates the banner as saying that the cornerstone will be dedicated "on Tuesday," a seeming mistranslation of "third" which in Hebrew is translated as "the third day." However, this photo is from last year, and while the Temple Mount Faithful website definitely wants the Third Temple to be rebuilt, it doesn't indicate anything special about today.The person most responsible for this lie is Sheikh Tayseer Tamimi, who incites Palestinian Arabs to riot literally every day. Tamimi, along with other sheikhs, are always warning about threats that simply do not exist, almost always centered around the Temple Mount. Most of their warnings get a little play in the press but a some of them take hold of the imagination of easily excitable Palestinian Arabs and they get the riots that they so passionately want.
Interestingly, while many Palestinian Arabs are credulous enough to believe Tamimi's and his cohorts' lies, the Arab media as a whole know by now that it is simply an exercise in incitement.
Palestine Today complains bitterly today that Arab satellite TV stations have not been giving any coverage to Jerusalem lately. They whine that the Palestinian Arabs have been warning about the danger to Al Aqsa mosque for a week and a half now, but the Arab TV stations do not have any shows about Jerusalem and instead air infomercials about miracle cleaning products. (They interviewed one anonymous employee who claimed that it was deliberate censorship as they have specific instructions not to escalate tensions with Israel and that it is a business decision. )