(V.50:39).
a) Narrated Qais: Jarîr said, "We were with the Prophet صلى الله عليه وسلم and he looked at the moon on a full-moon night and said: ‘Certainly you will see your Lord as you see this moon and you will have no trouble in seeing Him. So if you can avoid missing (through sleep or business) a prayer before the sunrise (Fajr) and a prayer before sunset (‘Asr ), you must do so’. ‘He then recited Allah’s Statement:
"And glorify the praises of your Lord before the rising of the sun, and before (its) setting." (V.50:39).
Ismâ‘îl said: "Offer those prayers and do not miss them." (Sahih Al-Bukhari, Vol.1, Hadîth No.529)
b) See the footnote of (V.32:16).