Allah, exalted be His praise, says: "And they were not commanded except to worship Allah, making religion sincerely His, inclining to the truth, and to establish prayer and give zakah; and that is the upright religion." [Surah al-Bayyinah: 5]
Along with it there are several other verses which mention the obligation of prayer.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحيض / Q1675