Ruling on Kissing One's Sister
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Question: Is it permissible for me to kiss my sister, or for her to kiss me?
Answer: There is nothing wrong with you kissing your sister or her kissing you, and likewise all your mahram (relatives one may not marry), such as your paternal aunt, maternal aunt, your father's wife, your mother, and your sister's daughter. You may kiss her on the cheek, the nose, the forehead, or the head if she is an adult. The Prophet (peace and blessings be upon him) used to kiss Fatimah when she came to him or when he went to her; he (peace and blessings be upon him) would take her hand. And al-Siddiq Abu Bakr (may Allah be pleased with him) , when he went to his daughter Aishah while she was ill, kissed her on the cheek.
Answer: There is nothing wrong with you kissing your sister or her kissing you, and likewise all your mahram (relatives one may not marry), such as your paternal aunt, maternal aunt, your father's wife, your mother, and your sister's daughter. You may kiss her on the cheek, the nose, the forehead, or the head if she is an adult. The Prophet (peace and blessings be upon him) used to kiss Fatimah when she came to him or when he went to her; he (peace and blessings be upon him) would take her hand. And al-Siddiq Abu Bakr (may Allah be pleased with him) , when he went to his daughter Aishah while she was ill, kissed her on the cheek.
Source
binbaz.org.sa
The Arabic text is copied verbatim from the original source, without any edits.