Abu Thumamah al-Hannat said: Sayyiduna Ka'b bin Ujrah (may Allah be pleased with him) met me while I was heading to the mosque with my fingers interlaced, and he said: I heard the Messenger of Allah (peace and blessings be upon him) say: "When one of you performs ablution and then comes to the mosque, let him not interlace his fingers, for he is in a state of prayer."
Hadith Referenceالمعجم الكبير للطبراني / باب الكاف / 16382