Shaylh Ibn Uthaymeen was asked the following question:

Question:

What is the ruling on fulfilling promises?

Answer:

“According to the mathhab, it is Sunnah and what is correct is that it is obligatory”.

[Kanz uth-Thameen Fi Su’alaat Ibn Saneed no. 760 pg. 175]

Translated by

Faisal Ibn Abdul Qaadir Ibn Hassan
Abu Sulaymaan