|The hadeeth, "Seek knowledge even if it be to China"|
Related by ibn Adee (2/207)m Abu Nu'aym in 'Akhbaar Asbahaan' and others via many routes of narration, and all of them adding the words "for indeed seeking knowledge is an obligatory duty upon all Muslims."
Ibn al-Jawzee mentions this and then quotes ibn Hibbaan saying, "invalid/rejected, it has no basis" 'al-Mawdoo'aat' (1/215)]
adh-Dhahabee also endorsed the above words of ibn Hibbaan, ['Tarteeb al-Mawdoo'aat' of adh-Dhahabee (pg. 52 no. 111)] and likewise as-Sakhaawee ['Maqaasid al-Hasanah' (pg. 86 no. 125)]
al-Albaanee declares this hadeeth to be maudu (fabricated) ['Da'eef al-Jaami as-Sagheer' (no's 1005-1006)]
In summary, the above hadeeth is related by a group of trustworthy narrators without the words "even if it be to China" and a few narrators who are deemed weak/liars/abandoned by the scholars narrate this additional wording. So the hadeeth with the additional wording is fabricated, but without is hasan (good). [See 'Silsilah ad-Da'eefah' (1/600 no. 416) for detail.]