וילן שם כי בא השמש (ויצא כח:יא)

Chazal teach us that the three times for prayer – morning, afternoon and evening – were instituted by our holy Avos – Patriarchs: Avrohom – Shacharis, Yitzchok, Mincha and Yaakov Ma’ariv.

While the first two Tefillos—Shacharis and Mincha—are obligatory, the Maariv prayer is “רשות”—one is not required to daven, but it is desirable to Daven Maariv. 

When reciting the Maariv prayers, do ask for whatever you wish for – even “רשות” – things that are nice and desirable.