What is the virtue of supplication, and is it prescribed for a Muslim to supplicate for his brother when asked?

Question:
May Allah reward you. The brother asks: What is the virtue of supplication, O Shaykh? And if a questioner asks me to supplicate for him, should I respond to him? And has anything been reported regarding this from the Salaf?

Answer:
Supplication is worship, as stated in the hadith. The status of supplication is great, and Allah (Exalted and Majestic is He) commanded it in many verses and promised that He will respond to it. So, supplication is the greatest of the types of worship. In the hadith: And if someone advises you to supplicate for him, supplicate for him, supplicate for him. The Prophet (peace and blessings be upon him) said to 'Umar (may Allah be pleased with him) when he wanted to perform 'Umrah and came to seek permission from the Messenger (peace and blessings be upon him), he said to him:
So, if your brother advises you to supplicate for him, supplicate for him, even if he did not advise you, you supplicate for yourself, for your parents, and for your Muslim brothers. Yes.