The initial evidence that the disciples had received the Holy Spirit was

The initial evidence that the disciples had received the Holy Spirit was speaking in tongues. This happened on the day of Pentecost, when the disciples were gathered together in one place and suddenly there came a sound from heaven like a rushing mighty wind, and it filled the whole house where they were sitting. Then, they were filled with the Holy Spirit and began to speak in other tongues as the Spirit gave them utterance. This was witnessed by many people who were amazed and astonished by what they saw and heard. This event marked the beginning of the spread of the gospel and the formation of the early Christian church.