Fisher, 38, went on Twitter over the weekend to share the adorable moment with his followers.
"Isaiah’s bed time prayer finished with 'Jesus thanks for going in the tomb and thanks for getting out all by yourself,'" Fisher revealed. Meanwhile, a proud Underwood replied to the tweet with a heart emoji.
Back in January, the couple welcomed their second child, son Jacob.
"Jacob Bryan Fisher entered the world in the wee hours of the morning on Monday," the country superstar revealed on Instagram at the time. "His mom, dad and big brother couldn't be happier for God to trust them with taking care of this little miracle!"
Underwood, 36, added, "Our hearts are full, our eyes are tired and our lives are forever changed. Life is good..."
The "Cry Pretty" singer shared several photos of her new bundle of joy. The first picture shows her husband beaming as he holds his newborn son while the second shows Underwood holding Jacob on her chest.
The third photo shows proud big brother Isaiah holding his new sibling.
Fox News' Sasha Savitsky contributed to this report.