Question: A writer claims what Ibn Taymiyyah said, "It is not necessary to make up missed salats. Instead of it, one must perform plenty of voluntary salats and do a lot of good deeds." Do good deeds replace salat?
ANSWER
Hadrat Ibrahim Muhammad Nashat states:
"All scholars have declared that it is a grave sin to omit salat and that it is necessary to make it up if one has omitted it. Ibn Taymiyyah said, 'A person who omitted salat deliberately does not have to make it up. It will not be valid if one makes it up. Instead of it, that person must perform a lot of voluntary salats and do many good deeds.' These heretical opinions had been put forth earlier by Ibn Hazm, too.”

Interpreting some Qur'anic verses and ahadith wrongly, Ibn Taymiyyah and Ibn Hazm departed from Ahl as-Sunnah wa'l Jama'ah and adopted the heretical position that good deeds would replace salat. This was one of the most harmful wounds that they inflicted on Islam. It is stated in a hadith-i sharif related from Hadrat Ali:
(If a person who has a salat to make up performs a voluntary salat before making it up, he has strived in vain.) [Futuh-ul-Ghayb]

All of the scholars of Ahl as-Sunnah wa'l Jama'ah say:
"A person who missed salat intentionally or due to an excuse has to make it up" (Radd-ul-Mukhtar, Halabi, Jawhara, Tahtawi).

"It is a major sin to perform salat after the prescribed time for it elapses if there is no legitimate Shar'i reason to do so. This sin is not forgiven when one only makes it up. After making it up, one has to make repentance as well" (Durr-ul-Mukhtar, p. 485).