The renowned Indian scholars Mawlana Abd al-Hayy Lucknawi called the kissing of thumbs, an innovation. The quote shows that scholars before the foundation of university of Deoband called this practice an innovation. The kissing of the thumbs remains up until today a sign of the Barelwis, who practice this innovation in their mosques:
Abd al-Hayy Lucknawi on Kissing Thumbs
“The fact is that kissing fingers while listening the name of the Prophet in Iqama and other places when his name is mentioned (may blessing and peace be upon him) is not proved by any hadith or athar. One who claims so is great fabricator.
So, this is abhorrent and henious bid’ah which has no base in the books of Sharia. One who claims agaist it, he has to produce evidence.” (Si’ayah vol. 1, p. 46)