Sayyiduna Anas bin Malik (may Allah be pleased with him) said: When the Messenger of Allah (peace and blessings be upon him) intended to write to the Romans, it was said to him (peace and blessings be upon him): They do not read a letter without a seal. So he (peace and blessings be upon him) had a silver ring made, and its inscription was 'Muhammad Rasul Allah' (Muhammad is the Messenger of Allah). Sayyiduna Anas (may Allah be pleased with him) said: It is as if I am looking at its whiteness in the hand of the Prophet (peace and blessings be upon him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب آداب القاضي / 20413
Sayyiduna Anas bin Malik (may Allah be pleased with him) said that the Prophet (peace and blessings be upon him) had a silver ring made, with the inscription 'Muhammad Rasul Allah' (Muhammad is the Messenger of Allah), and he (peace and blessings be upon him) said: "Do not engrave 'Muhammad Rasul Allah' on it."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب آداب القاضي / 20414
Sayyiduna Anas (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) had a silver ring made, with the inscription 'Muhammad Rasul Allah' (peace and blessings be upon him). He (peace and blessings be upon him) said: "I have had a silver ring made and had 'Muhammad Rasul Allah' (peace and blessings be upon him) engraved on it, so let no one else make an inscription like it."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب آداب القاضي / 20415