In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
1- When a Muslim prays he asks none but Allah and when he seeks help, he seeks the help of Allah alone. We pray to Allah, not to any creature, including the Prophets and Messengers of Allah.
2- There is no authentic hadith which teaches that Muslims should pray with the words “Ya Muhammad” and none of the Prophet’s Companions did so. So we should follow in their steps.
In his response to the question in point, Dr. Muzammil H. Siddiqi, former President of the Islamic Society of North America, states:
The Prophet Muhammad (peace and blessings be upon him) himself told us in a very authentic hadith that is reported by `Abdullah ibn `Abbas (may Allah be pleased with him), “When you ask something, you ask in the name of Allah and when you seek help, you seek help of Allah. Know that if the people were to gather together to benefit you with anything it would benefit you only with something that Allah had already prescribed for you and that if they gathered together to harm you with something, they would harm you only with something Allah had already prescribed for you.”
So the Sunnah is that we pray to Allah (Mighty and Exalted be He).
Tawassul means that in our duaa, we mention also the salat and salam (seek peace and blessings) for the Prophet Muhammad, or we show our love and our faith in Prophet Muhammad (peace and blessings be upon him).
So in this way, our prayer becomes more acceptable to Allah, but we must always pray to Allah, not to any creature, including the Prophets and Messengers of Allah.
There is no authentic hadith which teaches that Muslims should pray with the words, “Ya Muhammad”, and the Companions of the Prophet also did not do that and we should follow the way of our Prophet (peace and blessings be upon him) and his Companions in our prayers.
Prophet Muhammad (peace and blessings be upon him) was the last and the final Messenger of Allah. He is the beloved of Allah (Habibullah).
We believe in him, honor him, respect him and love him, but we do not worship him or come to Allah through him.
Allah Almighty knows best.