Adam Clarke on Matthew 23:29

Ye build the tombs of the prophets - It appears that, through respect to their memory, they often repaired, and sometimes beautified, the tombs of the prophets. M. De la Valle, in his Journey to the Holy Land, says, that when he visited the cave of Machpelah, he saw some Jews honoring a sepulchre, for which they have a great veneration, with lighting at it wax candles and burning perfumes. See Harmer, vol. iii. p. 416. And in ditto, p. 424, we are informed that building tombs over those reputed saints, or beautifying those already built, is a frequent custom among the Mohammedans.