Ata' (may Allah have mercy on him) said that a man asked Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) about kissing for the fasting person. He said: There is no harm, as long as he stops at the kiss. The man said: He took hold of her shin. He said: Even so, spare the fast.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8088