Sayyiduna Ibn Abbas (may Allah be pleased with them both) said that the Messenger of Allah (peace and blessings be upon him) said: "Whoever performs ablution, has done well, and it suffices for the obligation; and whoever takes a ritual bath, then the ritual bath is better."
This hadith with this wording is gharib (unusual) from this route; it is only known from the hadith of al-Hasan and others.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 1408