Musannaf Ibn Abi Shaybah 305 — Those who performed ablution whenever

Muhammad (Ibn Sirin) said: Sayyiduna Abu Bakr, Sayyiduna Umar and Sayyiduna Uthman (may Allah be pleased with them), as far as Abu Khalid knows, used to perform a separate ablution for every prayer. If they were in the mosque, they would call for a basin.