It is narrated from Imam Nafi' (may Allah have mercy on him): I saw Sayyiduna Ibn Umar (may Allah be pleased with them both) when a man beside him sneezed and said, 'Al-hamdu lillahi wa salamun ala Rasulillah' (All praise is for Allah, and peace be upon the Messenger of Allah (peace and blessings be upon him)). Sayyiduna Ibn Umar (may Allah be pleased with them both) said: "I too say: Peace be upon the Messenger of Allah (peace and blessings be upon him); but the Messenger of Allah (peace and blessings be upon him) did not command us to do it this way. The Messenger of Allah (peace and blessings be upon him) commanded us that when we sneeze we should say: 'Al-hamdu lillahi ala kulli hal' (All praise is for Allah in every state)."
Imam al-Tabarani (may Allah have mercy on him) said: "No one narrated this hadith from Sa'id bin Abd al-Aziz except al-Walid bin Muslim, and Suhayl bin Salih is alone in narrating it from him."
This is how it appears in the Dar al-Haramayn edition; the correct name is probably "Sahl".
Hadith Referenceالمعجم الأوسط / باب الميم / 5698
Hadith Takhrij«أخرجه الحاكم فى «المستدرك» برقم: 7786، والترمذي فى «جامعه» برقم: 2738، والبزار فى «مسنده» برقم: 5890»