Does one who, in a moment of anger, said to his wife, "I'm not praying anymore; I'm going to go become a Christian," commit an act of disbelief (kufr), knowing that he regretted it, sought forgiveness, and completed his prayer?

The matter is easier than what would necessitate emotional outburst and uttering the phrase "I left prayer and became a Christian." The husband did not actually abandon prayer, nor did he become a Christian, and his utterance relates to a future matter. He has regretted it and sought forgiveness. He must be careful not to repeat that and to renew his repentance.