The Prophet (peace and blessings be upon him) said:
"Give every surah its full due in bowing and prostration (that is, according to the length of the surah, spend a proportionate amount of time in bowing and prostration as well)."
Hadith Referenceصحیح الجامع الصغیر / حرف الألف / 1054
Hadith Gradingالألبانی:صحيح
Hadith Takhrij[ش] عن بعض الصحابة. صفة الصلاة ص ٨٤: حم.