What is the source of Sheikh Ibn Uthaymeen's ruling on kissing the Mus'haf?

Shaykh Ibn ʿUthaymeen said: "Kissing the Mus'haf is an innovation (bidʿah) and not a Sunnah. The one who does it is closer to sin than to safety, but his intention to glorify the word of Allah will be rewarded."

Scholars have differed on the ruling of kissing the Mus'haf; some considered it desirable (mustahabb), others permissible (mubaḥ) (which is well-known among the Hanbalis), and some disliked it (makrūh) (among the Malikis).

Some scholars hold that refraining from kissing the Mus'haf is more appropriate due to the lack of evidence for it from the Salaf. Imam Ahmad was asked about kissing the Mus'haf and he said: "I have heard nothing about it."

Shaykh Ibn Bāz believed there is no harm in kissing the Mus'haf, but abandoning it is better due to the lack of evidence, though it is permissible if done out of reverence and love.

Shaykh al-Albani definitively stated that kissing the Mus'haf is an innovation.