11. Do you know which Prophet's which dua that is accepted till date?

السلام عليكم ورحمة الله وبركاتة 

 بِسْمِ ٱللَّٰهِ ٱلرَّحْمَٰنِٱلرَّحِيمِ

Ibrahim [AS] supplicated, "Our Lord, I have settled some of my descendants in an uncultivated valley near Your sacred House, our Lord, that they may establish prayer. So make hearts among the people incline toward them and provide for them from the fruits that they might be grateful." [14:37]

This is the prayer Ibrahim [AS] supplicated when he left his wife Hajar and infant son Ismail (AS) near the valley of Mounts Safa and Marwa. Within few hours Allah send Jibreel [AS] blessed with Zam-zam and within few days send a caravan who settled down there along with Hajar. 

Ibrahim  [AS] supplicated the same dua the second time after the Allah's House was built in that place and its people lived around it. "My Lord, make this a secure city and provide its people with fruits – whoever of them believes in Allah and the Last Day.” [2:126].

Till date his dua is being accepted. In a valley where there is less/no agricultural activities, Allah made this place provided with all types of fruits that is available through out the world and through out the year.

Ibrahim  [AS] asked Allah to grant sustenance for the believers only. However, Allah answered, “And I shall still provide him who disbelieves with the wherewithal for this short life and then I shall drive him to the chastisement of the Fire; that is an evil end.” [2:126]. Allah has made this city a sanctuary (sacred place) the Day He created the heavens and earth, until the Day of Resurrection.

Allahuthala mentioned in other place of Quran: "Whosoever enters it, he attains security" (3:97) and, "Have they not seen that We have made (Makkah) a secure sanctuary, while men are being snatched away from all around them) (29:67).

الحمدلله