Abu Thumamah al-Hannat (may Allah have mercy on him) says: Ka'b bin Ujrah (may Allah be pleased with him) met me while I was heading to the mosque with my fingers interlaced. 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 prayer."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجمعة / 5882