Hi Light,
Lets look at all 3
Mk 13
13 As He was coming out of the temple [grounds], one of His disciples said to Him, “Teacher, look what wonderful stones and what wonderful buildings!” 2 Jesus replied to him, “You see these great buildings? Not one stone will be left on another which will not be torn down!”
3 As He was sitting on the Mount of Olives opposite the temple, Peter and James and John and Andrew asked Him privately, 4 “Tell us, when will these things happen, and what will be the sign when all these things are about to be fulfilled?”
Matt 24
Jesus left the temple area and was going on His way when His disciples came up to Him to call His attention to the [magnificent and massive] buildings of the temple. 2 And He said to them, “Do you see all these things? I assure you and most solemnly say to you, not one stone here will be left on another, which will not be torn down.”
3 While Jesus was seated on the Mount of Olives, the disciples came to Him privately, and said, “Tell us, when will this [destruction of the temple] take place, and what will be the sign of Your coming, and of the end (completion, consummation) of the age?”
Lk 21
As some were talking about the temple, that it was decorated with beautiful stones and consecrated offerings [of magnificent gifts of gold which were displayed on the walls and hung in the porticoes], He said, 6 “As for all these things which you see, the time will come when there will not be one stone left on another that will not be torn down.”
7 They asked Him, “Teacher, when will these things happen? And what will be the sign when these things are about to happen?”
Jesus had this conversation once, and gave it privately to Peter, James, John and Andrew....see mk 13:3.
Any one of these disciples would have conveyed the information to either Matthew, Mark or Luke to write it down.