Majma al-Zawaid 2237 — Reports on the awrah

Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) reports this saying of the Prophet (peace and blessings be upon him): "There is no harm in a man turning a slave girl over to look at her when he intends to buy her; however, he will not look at her 'awrah, which is the area between her knee and the place where the lower wrap is tied."
Al-Tabarani recorded it in al-Mu'jam al-Kabir; its chain contains a narrator, Salih bin Hassan, who is da'if (weak). Ibn Hibban mentioned him in the book "al-Thiqat".