"Ask Allah for everything, even the lace of your shoes. If Allah does not provide, it will never be available."Ibn al-Sunni, no. 349 - hasan. Supported by at-Tirmidhi 4/298 and others.
"Nothing is more honourable to Allah the Most High than du`a."Sahih al-Jami` no.5268.
"The most excellent worship is du`a."Sahih Al-Jami` no. 1133