Answered by Shaykh Faraz Rabbani
How is it to kiss thumbs during Khutba upon hearing the name of the Messenger of Allah (Allah bless him and give him peace) and reciting blessings (durood) upon hearing the Qur’anic verse instructing believers to send blessings (Ayat-e-Durood)?
During Khutba it is not allowed to perform Namaz or speak.
In al-Durr al-Mukhtar, with its supercommentary by Ibn Abidin al-Shami (2: 158) two it is mentioned that *1. When hear the name of Rasool ALLAH peace be upon him and Ayate-e-Durood neither kiss the thumb nor recite Darood Shrif because it is Fard to keep tongue silent (speechless), instead recite Darod Shreef in heart. This order is for only during Khutba on other occasions it is Mustahib to kiss thumbs upon hearing the respectable name of Rasool Allah Sallallahu Alaihe Wasslam. In Ibn Nujaym’s al-Bahr al-Ra’iq (2: 155) it is mentioned that *2. In the same book on page 156 it is mentioned that *3. In Fataw-e- Amjadia on page 286 in part one with reference of Hidaya it is mentioned that *4. The same is also mentioned in Fatawa-e-Rizvia on page 741 and 759 in part three. Allah Ta’ala Knows the best.
(Fatwa from Monthly Kanzuliman-India)http://www.islamicacademy.org/html/Fatwa/English/Khutba.htm