Is it obligatory for one who hears the mention of the Prophet (peace and blessings be upon him) to send blessings upon him?

The questioner:
Do you find that it is obligatory for one who hears someone say "peace and blessings be upon him" to say "O Allah, send blessings and peace upon him," or is it recommended?

The Shaykh:
He should do so; because the apparent meaning of the hadiths indicates that it is obligatory, due to his saying, "May the nose of the man who is mentioned in his presence and does not send blessings upon him be crushed." He cursed him, asking that Allah crush his nose. This indicates from it that it is obligatory, and that whenever he is mentioned to you, you send blessings upon him (peace and blessings be upon him). Whenever you hear his mention in a sermon, or in a gathering, or in a challenge among you, you send blessings upon him (peace and blessings be upon him).

The questioner:
Does he drink the morning drink?

The Shaykh:
All remembrance is among the causes; all remembrance of Allah and sending blessings upon the Prophet is among the causes of the rectification of the heart and the expansion of the prayer.

The questioner:
In the middle of the prayer.

The Shaykh:
As you heard about it. Yes.