Hadith: Verily, your Lord is Modest and Munificent. He is ashamed to turn down His servant empty handed when he raises his hands to Him

عن سلمان رضي الله عنه عن رسول الله صلى الله عليه وسلم قال: «إن ربكم حَييٌّ كريم، يستحيي من عبده إذا رفع يديه إليه، أن يَرُدَّهُمَا صِفْراً».
[صحيح] - [رواه أبو داود والترمذي وابن ماجه]

Salmān (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "Verily, your Lord is Modest and Munificent. He is ashamed to turn down His servant empty handed when he raises his hands to Him (in supplication)."
Sahih/Authentic. - [Ibn Maajah]

Explanation

This Hadīth is a proof for the permissibility of raising hands during the supplication. Raising hands is a means of supplication's acceptance, because it is a form of showing one's need, weakness, and humility before Allah, the Generous, the Self-Sufficient. It also symbolizes optimism that the servant will receive what he asked Allah for in his extended hands. Allah, the Generous, the Munificent, is ashamed to turn down His servant empty handed if he raised them to Him in supplication.